The resistors from cathode to ground on the output tubes were probably 1ohm “sensing” resistors. They allow checking of the bias on each tube “on the fly.” 1mv on a 1ohm = 1ma. The screen current will also be included in this figure so subtracting it is appropriate to get the plate current. ( plate + screen current = cathode current.)
Bought one of these in 76 I believe when I realized that JCM 800 was not going to be tolerated cranked up in any of the clubs my band was playing in. It did it all with the help of 3 pedals and the unique way I turned it into a channel switching amp with the ice cube. Of course I lost the tank reverb when I did that which I didn't use anyway. I used an effectron ADM 256 for slap back and verb.I still have all that shit. That big box Rat pedal was my marshal in a box. I played every damn thing from Hank Williams to Billy Idol thru that amp. It was worth every cent. I used up every inch of that amplifier and every watt it could spit out.
Not sure if anyone brought it to your attention or if you looked it up but 79's had GE "Fender Special" tubes in em. I just got a 79 push pull and it has all the original tubes in it. I got it for 400 bucks :) Great video man.
+The Guitologist I had just bought an Egnater Tweaker amp not long before and had to get rid of it because I just had no use for it anymore. I got the Deluxe from my friend's dad. I wanted it so badly after playing through it and realizing the guy hadn't touched it in years. I just showed up and offered him the 400 and he took the money with great enthusiasm. He even gave me a bunch of replacement tubes. Old JJ's, a winged C, some sylvanias, ei's. I've swapped tubes a few rimes but man those original GE 7025's in V2 (I play through the vibrato channel) are pretty great. I may have to pull the trigger on some old Blackplates though.
The 3 Capacitors that were replaced with the Orange Caps were put in there for a Mod to balance the phase inverter. Dan Torres from Torres engineering in California had some little mod kits he was marketing. He was selling matched sets because over time the blue ones tended to drift as well as the Carbon Comp Resistors, and you end up with a mismatched output. It was pretty common with the silver face amps. The ceramic disc caps from the grid to ground I think were there to protect the tubes from transient spikes... sort of like a shock absorber. They were supposed to be pretty transparent and not affect the tone.
Hi Brad. A cathode resistor on a fixed biased amp will increase headroom. At -35V bias and the cathode at 0V, the largest signal before clipping is 70V peak to peak. If a cathode resistor is used and the cathode is at +10V now the largest signal before clipping is 90V peak to peak. Obviously if the resistor is a 1Ω just for bias measurement then it has no effect on headroom.
Fender often put those ceramic snubber caps on the grids of power tubes to prevent parasitic oscillations, even though they aren't on the schematic, so they may indeed be stock, but no harm in taking them out if it doesn't oscillate.
Love your channel. I'm learning so much. I have a question about my 1980 Deluxe Reverb - (basically a Silverface with a black faceplate). It sounds just fine. However, when I turn it on I notice the tubes glow super hot for a second as the current runs through and then go dim. Is this an issue? I read somewhere there was an issue with how these amps were wired with respect to the initial current flowing through which could lessen the life of the rectifier tube. Any advice would be appreciated.
Have a 78 JMP with a 71 mock 1990.cab( pre Rola Greenbacks) and for smaller gigs a 79 DR! Love them both for different sounds! Got the DR and 88 Am St Strat for $1300 2 yrs ago! Bass rig a SVT and Ampeg BT cab with two 15's!
I am incredibly lucky I was able to purchase a pristine Deluxe reverb from a old friend of mine . It’s been in the closet most of its life . All original tubes , two prong chord , Im interested to know the exact year , AB763 . Sounds excellent,
Mine is 1978. It has the push/pull boost on the front, no Boost pedal input back side. I still have all the original Fender labeled tubes and the original blue labeled CTS speaker. I changed that all and keep everything. Now it is a really better amp. Especially the speaker was a really bad one. The original Tubes of the end seventies amps era are not good ones too in my opinion. My amp was like new. He was not played much. Now he sounds really great. He still has the original blue capacitors in 2018.
Cathode bias on power tubes will reduce the headroom compared to using grid bias power tubes? Cathode bias will break up the amplifier sooner compared to using grid biasing. Is this a general statement for all tube amplifiers brands and models. I know that the fender tweeds used cathode bias which makes the tweed amps have that fuzzy torn speaker and tube breaking up sound that Eric Clapton gets.
This is the same as my amp, bought it new in '79. I love the amp, but the original speaker was crap and it benefited greatly from a Weber speaker. Changing the PI coupling cap for the blackface value of .001uf also tightened up the tone. The bright cap could also stand to be lowered a bit in value in any event. I haven't done it yet, but the pull-boost is, as you note, useless as is, and ought to be replaced with something useful, like, say, a switch to break the mids-resistor-to-ground.
Where can I source those awesome pipe cleaner style brushes to clean those 1/4" jacks? I've just been using an old dummy plug with the cleaner in an attempt to clean those old contacts. For the tube sockets, I've employed those interdental cleaning brushes.
I'm noticing a trend of, possibly unintentional, masturbation references in your videos. They're damn sure good for a giggle, and you never outgrow that kind of humor. Thanks Buddy.
I got to thinking. It might be a first but with a GZ34 you might want to check your B Plus on your main filters. I'll bet it's awful close or over the rating of those filters.500 volt rating would be safer. You still da man.
8:41 did fender parallel those two caps on the right side knocking the voltage in half and doubling the value 44 uf at 225 volts the twin reverb is in series on the B+ with two 285v 100uf caps then choke followed by screen grid cap 20uf at 500 volts 4.7k follows 20uf 500v cap follows 10k and a 20uf 500v in the power supply.
The teflon wire and switches are poor quality on the new footswitches.The taper on the pushpull is kinda fast. I like to put tube retainers on power and rectifier tubes. I don't have luck with Chinese power tubes. I ran a 5AR4 in my Black deluxe with a replaced silver era power transformer. It sounded great. I started using JJ filters.So far so good. I've had real good luck with the JJ power tubes. I've been leaning towards the Tungsol 12AX7s.I love to take the boost pot and circuit out and install a good ! meg audio pot. I like to change the reverb drive cathode resistor from 680 ohm to 2.2 k with a 25 uf. .002 from control grid to ground on the power tubes is factory.Parasitic suppression to make up for sloppy factory lead dress compared to a Black amp,just like your ABnormal Bassman. It looks like Torres work on the cathode and screen resistors.Good choice for the 470 ohm screen resistors.Who put the power tube sockets in goofy? What were they thinking. I know it wasn't you.What I'm realy jealous of is that badass cigar box guitar.Smoking.Check out that Weber vst page bias chart. It's pretty cool.You got me hooked,Brad.Right On.
Great video. What speaker did the customer go with and/or which would you suggest? I have the same amp that was black faced in the vibrato channel and looking to upgrade the speaker. Thanks
+Tom Lindsay The customer had the original speaker reconed locally. If you have a local service, go that route for recones because shipping quickly makes it ueconomical. Eminence makes a great selection of speakers, so do Weber and WGS. Most importantly, they are among the best and are affordable if you live inside the US. If you're going for maximum cleans, go with maybe a Weber California Series or an Eminence Red Coat series. For more cone breakup, go with a power powered Weber Signature Series or an Eminence Legend 50w. Good luck with your tone explorations!
+The Guitologist Thanks for the reply, very helpful! I like the warmth of the Deluxe so am also considering the Eminence Cannabis Rex. I'm sure there are others in this tonal area. What do you think about the Celestions?
Celestions are good speakers, but living in Louisville, KY, I tend to gravitate toward Eminence, Weber, or WGS. They are all built close to me. Saves on overall shipping costs. Eminence, KY is just about 20 minutes from my house. And they all sound as good or better than equivalent Celestions.
+The Guitologist I understand. The speaker in it is a swapped, Fender Special Design Eminence (1258?) which I like and read a positive review by Bill M. on the forums about, so will probably leave it. Go Kentucky! Thanks for your beneficial help.
I've seen multiple reasonings... everything from a shielding thing (being near transformers) to strictly a protective measure for anyone that throws cords or other stuff in the back. I believe it's more the former, preventing electronic interference
this guy would hate me for what i did to an all original '74 Fender Twin Reverb. i had it totally redone to '65 Black Face specs as close as possible..extensive mods to get it to have a warmer deeper tone.. and so it would start to break up around 4 and a half volume,in a smaller room,that's as loud as i could possibly go..had the master volume removed,always hated that push pull knob. the middle pit on the vibrato side has a special pot in it..i dont understand how my amp tech did it, but its very touch sensitive, from 1-5 it has a middle like a Mesa..fro 6-10 is stock fender. i love the tone i get from it and to me that's all that matters !
Sorry I’m not a tech so genuinely curious here. But wouldn’t you wanna put in a rectifier tube that would lower the B+ rather than raise it? Say like a 5r4? Wouldn’t that be easier on the tubes which are already cooking to put out 22watts for 6v6s? And It was always my understanding that the older “holy grail” deluxes had lower B+ and that is why they sound the way they do. I guess I’m just curious the reason for the GZ34 swap.
@@shckltnebay correct, the tube charts show a Gz34. However, and Iv since confirmed, fender put out a service sheet in ‘68 to all its service centers instructing them to quit using gz34s and to instead use 5u4s moving forward. A well known tech actually produced this when I asked. So, in review, a gz34 puts out the highest b+ of all the rectifier tubes, Theoretically working the tubes harder if biased the same. Next would be a 5u4 then a 5r4 with the ladder putting out the lowest b+. The 5u4 and 5r4 do require slightly more current from the power transformer but the last 5 decades have proved that the old fender transformers can handle that without issue. I like to swap between a 5u4 and a 5r4 and see which gets me closest to 60s spec b+ on a silver fender
The GZ34 is the better rectifier in terms of solidly supplying voltage. The 5U4 sags more. The voltages are slightly lower also. But the current draw is higher, so it's less efficient and harder on the PT. 95% of players won't notice a difference while playing. But some may.
Nice work as usual Brad! When if you can get a chance , think you could send me a place where i can get all 10 pots. to replace on a fender super reverb reissue? I'd sure appreciate it . Im looking at nesstube for a few tube replacements on a traynor vc80 . replace with some new old stalk 6L6's . too. through them . theres very little info. inside. the super is totally virgin . im tthe first in there . im so asshamed .try pulling the control dials off thinking they were all just realy tite. had a perfect little screw driver to get in a side twist from chassy to beside shaft . i was not thinking much as i tryed to pry off every one only to finally sink in that there are screws to the shaft. being the reissue .,all the pots are on it's own circuit board and each one has side bracing to strengthen em. i took one the the four bent over tabs up and off one to expose the wiper. and theres a plastic stoper the eight of the shafts have maybe 30 to 70%mobility. and their so prestine too. Anyhow sure appreciate any info that might help me through.. been looking at the fender stores and they don't seem to help me locate them . maybe cheaper to buy separately. idon't know . been yrs. since i done much any of this stuff but i don't quite that easily. Cheers s
Antique Electronic Supply has all that stuff. Classic Tone should have something too, or Edcor. You could call Edcor and tell them what you have probably and they could point you to what you need. Their site is pretty friendly though. Any of those three.
6:35 as a tech I would never rob someone of their vintage rca or mullards if it sounds good or they test strong why be dishonest and put noisy microphonic rubys.
It's year 2020, month of April, with the great(?) Covid-19 virus raging. I am in year 59 of guitaring ... my feeling regards filter caps, is spend the money and put the best in there that money can buy ... they last longer and you won't have 'em fail on you on stage ... they just aren't that expensive.
