1968 Newcomb Pathfinder E-20 Converted to Guitar Amp......A Diamond in the Rough !!! 

Glad you like it, Brad. It really is nicely made and works quite well.

P

bills48321 You're right, Bill. I will definitely keep that in mind for a future video. Meanwhile you might enjoy the video featuring tone improvement in a Gibson GA35-RVT amp. The change in the Newcomb was similar, but not quite as pronounced.

+Jonathan Castillo Thanks so much, Jon. The camera microphone really doesn't do justice to any of the amps I record. Some day, I would like to step up to a camera with an input jack for a separate, better quality, microphone.

Thanks, Ronny. Conversions are a great way to start out learning about electrical circuitry.

Thanks for joining us, Jon :)

+TheRudydog1 Thanks so much, Rudy. Rusty and I really appreciate your kind words. Congratulations on the newly acquired Newcombs and best of luck with your restoration of them.

You're welcome, Sam :)

We're glad you enjoy them, Dan. Thanks for watching and commenting :)

Mad Dog, Ripple, and Country Club Malt Liquor were standard refreshments at all social gatherings back in the old days.....when "only the best would do" :) On a more sober subject, yes, the presets are very clever.....much better than the indelible ink lines you see scrawled on amps from time to time.

@@UncleDoug - COUNTRY CLUB! LOL! Yep, I remember that too. And Mickey's Big Mouth Malt Liquor. The ladies liked the Boone's Farm and Gallo Spanada.

You're welcome, Steven. Glad you liked it. Of all the PA conversions I have seen and done, this one was definitely one of the very best.

Thanks, Nixo. I'm glad you share my enthusiasm for the mighty Newcomb E-20. I'll keep your suggestion in mind for future modification. Don't build up Rusty's ego too much, his agent will probably hit me up for a big raise :)

Thanks so much, EB. Rusty is an essential element in our educational compound.

You're welcome, VR. Ultralinear OPT's are indeed excellent for acoustic guitar use.

Greetings, Mudy, and a big hello to all the viewers in Brazil. Rusty and I are glad to hear that you liked the video. Thanks for watching !!! :) ^. .^

Uncle Doug Always a pleasure, i quite enjoy your sense of humor as well - + really like it when you go thru the schematics Cheers

mudylafeet Thanks again, Mudy. I hope Rusty and I can keep you laughing, and that the tech discussions continue to make schematics easier to understand. :)

Wow....Congratulations, Mr. P. It sounds like you hit a sonic home run !! I hope the mighty Newcomb gives you many years of great service.

@@UncleDoug Thank you Sir

Thanks so much for your very nice comments, Dwight.

Thanks, BT. I'm glad there are others who appreciate good, old-fashioned point-to-point wiring. It is indeed an art.....and (unfortunately) rapidly diminishing.

Let's hope we can keep point-to-point circuitry alive, CH.

Congratulations on a fine acquisition, VTA :)

Thanks, Peter. Our best to you :)

Congratulations on a great acquisition, VR.....and at a very reasonable price. They are wonderful amps. Best of luck with it.

Thanks so much, TA :)

Thanks, Kal. I'm glad you enjoyed the video. I thought Rusty really outdid himself on it :) ^. .^

Thanks, GS :)

Thanks, Jack. As my old granny used to say, "Everything in moderation."

Thanks, Rosie. Glad you liked the video :)

Thanks, JT.

+Wayne Bjorken Thanks, Wayne, and regards to your pups :)

I agree, AA :)

I believe you, KT. Thanks so much for the nice comment and input.

Sounds like a great set-up, Steve. Thanks for your input.

You're welcome, Roger. Rusty and I are glad you enjoyed the "sundae" :)

Uncle Doug Check me on this, but the Newcomb uses a split load phase inverter, right? See, I learned something....

Yes, indeed, Roger. Looking at the schematic of the E-20, the top center tube is the Phase Inverter. Its plate drives the grid of the upper output tube, while its cathode (opposite phase) drives the grid of the lower output tube. It's also known as a Cathodyne Phase Inverter. Good call !! Now for a second test, take a look at the Newcomb Model G-12 schematic (either in my video on this model or download it on the Internet). Same manufacturer, but what type of P.I. does it use? Warning: It's a little tricky.

Uncle Doug I think it's a paraphase, because it splits the signal coming off the 6SF5 tube plate and sends it: 1. to the first power tube, and 2. to the 2nd 1/2 of the 6SC7 preamp tube's grid and then connects that plate to the 2nd power tube. And there's a resistor going to ground just before the signal hits the V1 grid, to bring the signal down in balance w/ the other signal. The 6SF5 has only one triode, so it couldn't be used to do both sides of the phase inversion; but the other 1/2 of the 6SC7 was available. I suppose one could connect the 6SF5's cathode to the cathode of the 6SC7 and get a long-tailed pair PI?

Roger Taylor I read up on the 6SF5 here: vinylsavor.blogspot.com/2013/04/tube-of-month-6sf5.html

+joohop Thanks :)

Thanks, CG :)

You're welcome Uncle Doug.

Me too, V. I like your kitty pic......it looks just like Jacky.

Walter Stahl I hope your recollections are good ones, Walter :)

I guess if it's a square dance where someone is calling out the steps, midrange would suit vocal clarity.

Good luck with it, LK. They make a really nice guitar amp.

+Joel Thomas Thanks, Joel.....glad you liked it. I bought the spray paint many years ago (and it still works !!) when I was restoring vintage jukeboxes as a full-time business. Back then, all sorts of original and good reproduction parts were readily available. Now, due to the decline in enthusiasm for old jukeboxes, the availability of parts has dwindled.

Wow.....thanks so much, Duke. Welcome aboard !! I was a teacher for many years and would (from habit) use old phrases like "snazzy", "what a drag", "I'm hip", etc. during classroom discussions. The kids loved it. I would hear them later using these terms on the playground. Good expressions never die, they just skip a generation :)

Uncle Doug Thanks for the reply. I just watched your 12 amp comparison video. They were all "snazzy" but the Kustom was downright "boss". Wish I still had mine! It's sad they were "frowned upon " back in the day.

I guess because they're transistorized rather than tube, some people looked down on Kustom amps, but quite a few famous musicians used them on stage. I just love their looks.....completely unique (and "far out") :)

So true. Back in the day they weren't "vogue". You were so "uncool" if you had one.

Thanks, Wayne.

+Jonathan Kosyjana Thanks, Jon....glad you liked it :)

ohh yeahh way cool,your channel kills it! thanks for your videos, i've already learned alot!keep it up =]..you dog is awesome by the way

You're welcome, Jon. Rusty and I appreciate your kind words and wish you the best :)

Rusty has always kept me on my toes......and occasionally other parts of my body, when I trip over him as he naps in the workshop :)

Uncle Doug, There is an amp that has been in my dad's attic for as long as I can remember. With it, is a metal plate with oiling instructions and indicates it is a Hammond model M amplifier, serial number 11836, 115 volts AC, 60 cycles, 93 console watts. There is one larger transformer that has no corrosion, as well as a smaller one, also without corrosion, that has AO-20936-0. The tubes look okay, and are as follows: 5U4, 6BA6, 6V6, 6V6, 6SC7, 6J7, 6J5, & 6SJ7. On the "front" are various screws, that look like wires have been attached, as well as a couple of what looks like RCA inputs. The best I could read with my old man eyes: "Pedal Cutoff" "Key SW" "Decay SW" "Sus SW" "Pedal In" "Voice Coil" "Ped" "Att-Key" "VIB"(?) The RCA looking inputs have (best I can tell) "Radio Phono" & "Spec Input" So……would this make a good guitar amplifier? I know absolutely nothing about electronics, but do play guitar, and love the different colors and temperatures of tones that tubes can produce. I am not asking how to do what needs to be done, because I am sure I will be finding someone to be with me every step I take…..I've just not seen anything other than amplifiers from M3's, M2's, or M100's anywhere. I DID, however, find the schematics, block diagrams, wiring for the organ itself….but what is the amp called? AO-20936-0??? Thanks, and sorry for asking so much ! Ke & Ri

+PeterDad60 Thanks, PD....glad you liked the video :)

Indeed. They are getting a little pricey lately.

Greetings and thanks, Flip. I agree, the tone is indeed "Fendery". These E-Series Newcomb PA Amps make excellent guitar amps....and at a bargain price.

Depending on the frequency of the hum, it may or may not be a tough one to repair, Mr. P. Good luck with it.

@@UncleDoug FIXED! WOOHOOO! Using a tube preamp/compressor it works great plugged into the Aux input. Thanks for inspiring me to get back into TUBE Heaven.

@@MrPiperian Congratulations on a successful solution to your problem. Best of luck.

Thanks, Mikael......glad you liked it :)

@@UncleDougYou know, I still have my Newcomb D-10 that I need to recap and make into an instrument amp. That i have both guitars and basses and would love to be able to use it with both. I'm thinking that clean, hi fi tone would give some sweet, clean tones for a bass.

Yes, it would.

Thanks, Stephen. Close. It was my amateurish rendition of Green River :)

I'll bet it does sound great, Dan :)

Those would have an even wider range of frequency reproduction capability than guitar amp speakers (at least theoretically -- more octaves). More likely, such speakers would do fine in either instrument amp. It's the voice speakers that are so disappointing.

I must agree that they are definitely drool-worthy tubes :) I would hate to see the total bill if you had to buy them from a premium tube supplier.

Do you know if there's any truth to the rumors about people like Aspen Pittman going to Russia and China and getting them to upgrade their designs and literally reverse engineer the old American and European tubes? I've been told that the new Mullards and Tung-Sols are very good re-issues, but I haven't tried any of them yet.

I have not heard these rumors, but from experience, I feel that many of the newly manufactured tubes are of excellent quality, often with superior power handling capability (higher plate voltage and current) when compared to vintage tubes. Some of the early "replica" tubes (i.e. from 10 to 20 years ago) were not so hot, but I think they're getting better and better at meeting and exceeding vintage specs. This is probably due to the huge, renewed interest in tube amplifiers and the large amounts of money being spent on them (and tubes).

Greetings, Cat. I'm glad someone out there shares my slobbering enthusiasm for high quality, original, vintage tubes. More and more often, I am encountering modern replacements instead of original old RCA's, G.E.'s, etc. You could probably debate all day over whether there is really that much tonal difference between old and new......I tend to think there really is a (sometimes subtle) difference.....but finding original tubes in an amp always impresses me as strong evidence that the amp was never altered, mistreated, or excessively used. It's like finding a smooth-running, all original, Power Pack 283 under the hood of a '57 Chevy......instead of a crate 350.

Uncle Doug Sorry here but these days are gone. The market for real *good* NOS USA/JAN/German/UK tubes is about to its final close. Prizes are "through-the-roof" already. As the prizes rise some fellas tear out the Original tubes and smash it on ebay to make fast money, and sell the Amp some two weeks after without tubes to get the max$$$ out of it. For Years a´m looking for a "Jörgensen" all tube organ, its sound generator is made out of 48 ECC83 TFK tubes originally, but all i see is that some units apear on ebay they shorty rise above $1k and up. just because these tubes are in it. the winner tear out the tubes and *dump* the beauty organ *DAMN* And some NOS telefunken EL34 which I bought recently are not as good as new JJ. So what? My two cents are: there is a chance to get some good NOS tubes, western made. But i´m entirely out of this by now. As i´m very happy with new made JJ when it comes to standart tubes. When buying NOS or odd (non standart) tubes i´m always go for formally USSR types. As I found that they are much more rugged/reliable than any other (=similar) types. For instance I use GU50 (ry-50) which is the russian version of the LS50 (EL156). Where one can get the ry-50 for about $5 but the NOS europe is about $100-200 and you´re not knowing if they are really NOS or just claimed like it.... If a ry-50 fails, i *do not care* i just swap it. But with a EL156 i go nuts ;) But my 4x ry-50 Amps still got the 1st set and its doing just fine. So i´m replacing all my vintage tubes with russian equivalents. Like 807=g-807 (g-807 is even more rugged than the original US made JAN-807) or EL34 is 6P27C, EL36=6P31C and 6L6=6P3C and EL84=6P14C(-EW which is happy with 400V). Or even use tube with *no* equi like the 6C33C regulator tube. My daily HiFi Amps are Philips EL6435 (4x PE06/40N output tubes each) which cost a little fortune NOS. But replacing them with G-807 and rebiassing these Amps just work fine and I do not need to wear out the PE06/40N tubes. A set of 20 (!!) G-807 is equal to *one* NOS PE06 in terms of the prize to pay for ;)

Uncle Doug i'm a sucker for old tubes, mostly just because _they look really cool._ i think there might be some truth to the idea that some old tubes sound better than new-manufacture, although i think that probably has to do with build quality and QC (i'm sure some of the new tubes are cheap for a reason.) don't get me wrong, i love digital stuff and i'm a gadget nerd. but whether the tubes work or not, i find something really artistic about them and i could stare at them for hours. there's quite an aesthetic appeal to them!

I've never felt that the benefitof such multi-purpose wiring was worth the effort, Bubby. If you set up such a circuit, let us know how it turns out.

+Michael Fearnley Very interesting. Thanks for the input, Michael.

My pleasure. I would recommend putting the PI into see saw operation instead of cathodyne for best overdrive performance, doing this gets rid of the grating anode voltage spikes on the cathodyne configuration (which will mess up the smooth OD of the UL configuration) as the cathode load goes into positive bias and conducts. You also get the benefit of reducing the cathode to heater voltage, reducing hum and improving valve life.

SuperCarver2011 Thanks, SC. If you're speaking of the final two tunes, they were similar versions of something I made up, with a little flamenco flair. Rusty helped me compose it :)

Uncle Doug Your trusty K-9 sidekick is very talented. However, I presume he doesn't sing along when you play those "Dog-gone blues"..LoL. I get a kick out of seeing the look he gives you when you ask him for any assistance.

Rusty is an excellent musician, assistant, and source of inspiration......but may seem reluctant to pitch in with the menial tasks. It's just his "video persona". In real life, he is a tireless worker ;)

Uncle Doug Lol! You and Rusty are "killing" me.

+Cass Virgillo Thanks, Cass. I had to visit Walgreens too, but it was for some Depenz, rather than BP meds :)) Glad you enjoyed the concert and the lurking Current Limiter. Happy Holidays !!

Greetings, CB. Your idea of adding tweeters is an interesting one, but the main deficiency with these speakers is bass.....there isn't much at all. The tone of the original speakers reminds of the piped in "music" at McDonald's or the (endless) paging at Home Depot. Being old fashioned, I tend to like a lot of warmth and bass in my guitar tone, and the only way I could get it was to shift to a more guitar-oriented speaker. I really appreciate your time, interest, and input. Thanks so much !!

Uncle Doug Just curious - is the frequency response of the speakers low end capability more a function of the circuit elements as they're configured or the speakers themselves? Granted they are old, but I can't help but think that 12" ceramics of this quality can't handle a little bottom? I'm not talking that windstorm generated 6 inches off the floor bass which causes building foundations to decay. . . perhaps as an acoustic-electric guitar rig or, dare I suggest, violin?

TheCarablanco A good question, CB. I think it's the speakers themselves. I really tried to use the original speakers, but they simply can't cope with the bass frequencies that a guitar generates. The ceramic magnets are rather small and the cones suspension is a little flimsy. They tend to flap around and sound pretty bad, even at moderate volume. I think the proof of this is that when the same circuit is connected to a large-magnet, firmly suspended 12" guitar speaker.....it sounds great.

Glad you like it, Jay.

You're welcome, V. You have a good ear. I was using a 1950's 12" Alnico (probably Rola) speaker, which does sound much like an early (tweed-style) Jensen. If I were to build this chassis into a combo amp or build a cab for it, the P12Q would be at the top of my list for speakers. Thanks for your input !! :)

Uncle Doug A huge YES! to the Rola speakers. I have a small collection. A very nice alternative to the Jensen's, at least in in Hammond's mind, as these were used as an alternate, and definitely not inferior speaker in their organs. The 8" Hammond Reverb Rola speakers are among my favorites. I'm looking to build a mini 4X8" cab with these. Ooooops, maybe I said too much :(

Thanks, CA. I found that old Natco movie projector/PA speaker in a local pawn shop and have been using it as my shop speaker for many years.

Greetings, Jim. It's always best to tightly twist the AC wires to the tube heaters, and when you get to the tube, don't wrap around the perimeter of the tube base, but arch up, over, and straight down to the pins to which you are soldering. Good luck with your project :)

Greetings, Slog. Congratulations on acquiring a great amp. I am completely impressed by every product I've encountered from Newcomb.....the amps are beautifully constructed and sound great. Here is an excellent site to explain the process of output tube removal: www.premierguitar.com/articles/20713-ask-amp-man-removing-output-tubes-to-reduce-power I think you will like the cathode bypass modification. I have no personal experience with the E-40 model, and really have no other modification suggestions, simply because other than sounding a bit sterile (which is improved by the CB cap) the amps have wonderful tone as-is. Best of luck with your new amp !!!

+Congi Thu Thanks, Congi :)

Yes, they were already there when I got it.

You're welcome, Donny. I really can't answer all your questions without evaluating the circuit.....so I think you would be better off trying the changes you mentioned, seeing if they work, and modifying them if they don't. This is, by far, the best way to learn.

+James King Rusty and I have posted 121 videos so far, James, and a bunch of them discuss all aspects of tube amp circuits....how they function and are designed, built, tested, etc. as well as all sorts of safety tips. I suggest that you watch some of them and see if they are helpful. Good luck :)

Each of the preamps is set up to accept a low voltage (i.e. less than 1V) input. If you placed them in series, the second preamp would receive a signal of much higher voltage than it was designed to accept. This would result in all sorts of distortion, as you suggest,.....but none of it would be of the "good" type.

I would assume that the unusual pre-amp tube plus the UL OPT definitely contribute to the unique tone, Mr. P. It shouldn't be too hard to clone.

tgitarezam b I believe that in any well-built amp circuit, all AC wire pairs should be twisted to reduce hum, TG. Perhaps some builders skip these details, but like any complex undertaking, there is only one way to do it right.

Yes, it would.

It does have a "jukebox-amp look", TC. At least the modifications were rather superficial and easily reversed. Thanks for your input :)

***** Thanks, Roger. I think I'll use it as a head. I have some good speakers in cabinets that work well with it. The original speaker cabs are open-backed (no bass resonance) and rather cumbersome, especially if good (heavy) guitar speakers were installed.

I think this unit was intended to be used for speech amplification at sports or at a faire. Therefore there is no need for any bass responce. Open baffle makes the unit more lightweight thus easier to carry the whole thing around. The cones of the speakers are special designed for it. You can see this by looking at the very small ferite magnet as well. It´s intended to be used only in (lo)mid to high frequency range. But with a very good efficency, well over 100dB SPL at 1W/1mtr. is typical for these speakers. If you mount a guitar speaker into this sort of cabinet it will sound awful and you´ll may end up with a blown/damaged speaker due to too much cone excursion at low end frequencies. Use only the Amp like a Head is the best thing you can do. But some Harp players will love this thing with its original speakers, because this is exactly what they are looking for. This old PA units match exactly their needs in terms of frequency response and overall sound feeling...

Thanks for the excellent and informative input, TC. Your recommendations coincide quite well with my planned use for the unit. I was, however, unaware that the tone response of this system was so suitable for harmonica use. I'll keep that in mind when seeking a new owner for it. Thanks again for your time and assistance :)

You're better off using a pot and making the NFB loop adjustable, Jonny. You're welcome :)

Greetings, Tom. I've never owned a Bogen amp, but I understand they are of very good quality. Sorry about the bad tubes, but for $50, you still hit a major home run :)

I have read the low max-PV values for 6BQ5's and 6V6's in the tube manuals and am puzzled by them, since both tubes routinely operate at much higher plate voltages than the manuals would suggest. Indeed, Fender ran the 6V6's in their BF and SF amps at well over 400V. I would suggest that PV does not determine tube life, but rather it is Plate Dissipation that is the most important criteria. As long as you keep the PD below the max for any output tube, it's useful life should not be reduced.

I just ended picking up a Multi Kord Model 125 single ended amp which appears to be from the 50's maybe? Looks to be in very nice original condition except the speaker cone is shot. Appears to have original everything else in nice shape. I actually picked this up with you in mind and would like to give it to you for all the help and kind assistance you provide to everyone in your channel. I'm an old car dog like you and have restored a lot of cars (that's why I knew so much about the 70 Mustang Boss 9). In any case, this amp seemed like the kind of thing you like and it would be my pleasure to send it to you to do with as you wish. Bert

Thanks so much, Bert. If this is purely a tube amp (no semi-conductors at all) with a power transformer (not series-filament) we would love to receive it and possibly use it for a video. Please provide your e-mail address and I will contact you directly.

@@UncleDoug I've tried to add it here twice, but the message disappears. My guess is they are filtering it out. I've added it to the "about" column on my information. Let me know if you can get it from there.

Yes, I was able to retrieve your e-mail address and will contact you at once.

I'm relieved, TM.....I was worried that you might describe something complicated and hard to understand ;)

@@UncleDoug Lol the way i describe things is convoluted .I could describe making buttered toast and half the people reading it would swear i somehow connected it to the signing of the " magna carta " lol..I don't have your gift of uncluttering an explanation !

@@toobmaniac Thanks, TM. It comes from years as a math and science teacher.

Virtually all the schematics I use in the shop and in videos are simply downloaded from the Internet. A Google Search can turn up the schematic to just about any amp ever made. Give it a try.

I'll bet it would, Roger.

I do tend to under-drive the vintage amps, generally to protect the original speakers. I did crank up the Newcomb to see what would happen, and it took quite a bit of input signal and amp volume to get any sort of distortion, probably due to the ultra-linear OPT. It was simply too loud to record effectively with my camera microphone.

Uncle Doug If you drive a ultralinear amp into distortion, it sounds awful. All because the OPT is "too good" it cancels out nearly all that sweet k2 harmonics and let the odd k3 harmonics be heard. That is due to how the UL-OPT works. The Screen grid taps not only reducing the voltage they also act as a negative feedback both for voltage and current. -- hence lower the output impedance of the circuit and also rises the damping factor -> better speaker control of the Amp. First done in the "QUAD-II" Hi-Fi amplifier. One of the best amp topology and circuit design beauty as well. For an Instrumental Amp you can simply disconnect the UL-Taps from the screen grids and wire them using the "old-fashioned-way" to the HV via screen grid resistors. If you like, you can make this modification switchable. This is done a few times in some "Mesa-Boogie" Amps. As the UL is best for clean sound or even with acoustic guitars while the classic "screen-resistor-hv" is best for overdrive. Hope this putts a little light on the UL design ;)

Hopefully, with the help of my, and other, videos, you can do the conversion yourself, MJJ. Give it a try and see :)

It does seem like a wise engineering modification, Fra, but since heat rises, one could question the benefits of holes around the tubes. The main source of heat is above the chassis surface, not within it. I can see no reason why it would reduce the shielding of the circuit.

​@@UncleDoug Thanks for answering. Depending on the amp chassis i think it might because of the laws of thermodynamics. A Fender style amplifier (or other brand) with the amp chassis in the top of the cabinet wouldn't benefit much i'd imagine as it would actually allow heat into the chassis but i think a bottom loaded Marshall style head actually would. Those regularly have a screen in the back or top of the head cabinet for the heat of the tubes to escape trough but no real way of sucking in cool air. The rising heat escaping trough the top/back would create a vacuum sucking fresh, cool air in trough the bottom louvre/screen and trough holes around the tubes in the chassis. I might be overthinking this and overestimating the added benefit but it does seem like a good way to cool the capacitors and tubes somewhat in small box head amps. I thought a lot about this subject because i hope to one day build a 5f2a based Princeton style circuit but in a Marshall head style chassis and cabinet as small as possible... About the size of, or, a little wider than a normal sized amp handle and was planning on using vents and holes because with a P.T, OT., choke and tubes producing heat in such a small housing i figured i could use as much cooling as possible.... If it ever happens that is..., i'm better at planning and thinking about building things than actually doing it i guess... but i digress and waisted enough of your time you could be spending on making these awesome videos already. Thanks for listening to me rant and have a good day.... give my regards to Rusty and Jack.

No problem, FraJa. Your rants are always welcome here :)

Glad you enjoyed it, SND :) We try to throw in a little levity to make the technical parts easier to tolerate. Regards to both of you from all of us in Rusty's Madhouse :)

The RickTone Tremo Boost can easily overdrive an amplifier into saturation. You don't need to add anything to the circuit. It can also create a Tremolo effect at the same time, if you wish.

Greetings, Andrew. Fine tubes......like fine wine.....always intoxicating :))

You can't keep everything, Joe, no matter how hard we try :)

+Jonathan Castillo I have no way to host such a photo, Jon. Perhaps you take a photo of the screen at 9:20 ? I have tried this is the past and it generally works fairly well.

Greetings, Sorin. A "guitar friendly" speaker would have a larger magnet, a larger diameter voice coil, and a firmer suspension around the perimeter of the speaker cone, to better cope with the bass frequencies that a guitar produces. This is especially important in open-back cabinets (such as these) where there is no trapped air to moderate the excursion of the speaker cone.

Ben Morris Thanks, Ben. Actually the amp had very effective bass and treble controls that required no modification. Overall, Newcomb electronic devices are of excellent quality and occasionally available at yard sales for very reasonable prices.

Very strange, Vince. I have never seen an E-20 with any components plugged into those sockets.

I checked it out again, and yep, they’re transformers . It shows a pin out and part number on them too. I can PM a picture if you like. Just searched via google “tr-91 Newcomb”. You can see and image of one there as well.

I did the search and you're right, they are input transformers for microphones. I guess they alter the impedance of the circuit to suit a microphone. They also seem to be rather valuable......so you are a lucky guy.

Uncle Doug, if it does not affect guitar output in a good way, I may keep them unplugged for now. I will try both ways once I put in the 50mfd 100 volt cap that you have added as well.

Let us know what you discover, Vince.

The power transformer puts out several voltages (see my video on Power Transformers). One of them is the high voltage, usually around 400V, that is applied to the plates of the output tubes (and other tubes, but at lower levels). Before it is applied to the plates, it has to be rectified into positive Direct Current, or else it would cause a loud 60 Hz hum. This rectified, positive DC high voltage is called the B+ voltage, by old timers (like me), because in early, battery-powered radios, the high voltage came from the "B" battery (there were two other batteries, the A and the C) and you connected the tube plates to the positive terminal of the "B" battery. Thus the DC high voltage to the tube plates was called "B+". We still call it that out of habit, even though the days of battery-powered antique radios are long gone. I hope this makes sense. Thanks for asking a good question.

I'm sorry, Mr. P, but it was sold to a viewer. Maybe you'll get lucky on Ebay.

@@UncleDoug That amp, thru 2 Weber Blue Pups? Clarity, Definition, Chime and Jangle for DAYS!

Indeed, Mr. P. The viewer/buyer of the amp still raves about its excellent tone.

@@UncleDoug I had a tech gut it, leaving me only vol. ctrl and an On/Off switch. Used it to push 2 Weber Blue Pup 10"s, and went to Glass Chime and Jangle heaven. I'd luv to get one of it's big brothers with 4 X EL 84. I think the magic is the 6BR8 and that ultralinear transformer.

Greetings, Scott. As I recall from my jukebox days, the MA1-L6 amp was used in the Seeburg "Trashcan" amps from the late 1940's. There was a later HFMA1-L6 (High Fidelity) amp used in the 1950's 100-R, C, J, etc. models. I found the following schematic, which seemed rather legible: www.4tubes.com/SCHEMATICS/Music-amps/Seeburg/ma1-l6.jpg

clearview02 it's SAMS 249-9, if you have access to it...

clearview02 You can use alligator clips to (carefully) test different value bypass caps, in parallel with existing bias resistors in the pre-amp and output tube(s). I usually start with 25uf @ 50V and see if I can hear improved tone and volume. It's a trial and error procedure, using different cap values in different locations, until you come up with a tone that you like.....generally warmer, with improved bass and gain.

Uncle Doug Thanks for your suggestion and many informative videos...i went back and watched your video on cathode bypass capacitors again--a lot of material there!...i did much the same experimentation on a PCB amp that had intermittent signal issues...disabling both the effects loop and footswitch circuits took care of the intermittent issues...i was surprised how much the signal "opened up" after disconnecting the effects loop...all those extra capacitors and resistors took a lot of "fizz" out of the sound...after that mod, i experimented with different value capacitors, to get a tone i like...but i didn't use the alligator clips, so i got lots of practice with my soldering skills!..i read somewhere that a lot of Fender's classic amp circuits from the 1950s came about from pure experimentation; as Leo was an accountant, not an electronics engineer, by prior training and vocation......

clearview02 p.s. and i wonder how much effect the mid-range driver has if you tweak the other elements as needed??...i know that Peavey used to put mid-range drivers in their tube guitar amps...Chip

Somebody is pulling your leg about Leo Fender, Chip. He was a highly experienced radio repairman and electronics whiz, who personally developed the guitars and amplifiers that made his name and company famous. In fact, he was so focused on the technical side of his company that he often neglected sales and accounting. Re the mid-range driver, most guitar amp tone circuits tend to scoop out the mid-range, because guitar pickups tend to emphasize this portion of the audio spectrum. Since we virtually never see popular guitar amps with mid-range speakers, I would tend to think they are not much of an asset.

+Shaman Man No.....if your output "wants" 16 Ohms then you could only connect to one 16 Ohm speaker, two 8 Ohms in series, or four 4 Ohms in series, i.e. the speaker load has to equal 16 ohms.

Uncle Doug Thank you so much for preventing a $200 dollar disaster.

You're welcome, SM. Glad to be helpful :)

Thanks, Amo.

Thanks for your input, Lost.

Amen, Liz. Double-sided boards, whether PCB or eyelet, are a nightmare to test and repair.....especially if they are held in place with wires running from them to the rest of the circuit.

Thanks. Probably around 18W.

@@UncleDoug if I Had An Old Turquoise Radio I:d Make A Bluetooth Speaker Out Of It

@@rogertyler3237 I'll bet you would, Roger ;)