Terry, this is one of the best videos you have done because you are troubleshooting live and not telling us what you did but showing us. I learned just today that there is a huge difference between troubleshooting and shotgunning..... good stuff bro
I love watching you work. You remind me of my father, Master Sargent Stanley Sikorski, Sr. USAF, who was a highly skilled electrical engineer and teacher at Chanute AFB for much of his career. He's no longer with us now, but watching you brings back memories of his methods and skills when he was working around the home shop.
It is a pleasure to listen to a person who is experienced and knowledgeable in regards to amps rather than the self appointed "experts" who dish out technical gems of knowledge that, with absolutely no technical background, they have gleaned from other so called "experts" with equally limited tecnical knowledge. Please keep these videos coming - they are awesome!
Terry, I love all of your videos, but this was ESPECIALLY valuable because it was in real time but because things were not straightforward. thats how it is, in real life. Whenever I go to repair something, there are always things that dont conform to spec. thank you very much! Wayne
RIP Aspen Pittman. Have the very same edition of the Tube Amp Book. Aspen signed it "Keep your pins straight, your sockets tight and never lose your bias." Great advice. Btw the owner's story mentioning "Hollywood" and "GIT" raise alarm bells. This was likely a tweed Princeton kept in one of the study rooms at the second Guitar Institute location in Gower Gulch.
When the output transformer of a tube push-pull power amp stage is connected-up improperly, it basically transforms the power amp into an even more powerful oscillator due to the negative feedback network becoming a positive feedback network.
Terry, I loved the long video of you talking through the faults and troubleshooting live. Very, very good! I am looking forward to more. Greetings from sunny Australia!
Cool that your story time reading is from Aspen Pittman's great book "The Tube Amp Book". He passed away just a week ago. RIP Aspen. G.I.T. 1981, is that Guitar Institute of Technology? Established in 1977 by guitar great Howard Roberts and Pat Hicks. It's now called Musician's Institute (MI) and has contributed to the education of many players over the years.
It's actually pretty normal, although usually on higher power amps. Output transformers actually make quite a lot of noise, it's just that you don't normally hear it at all because the speaker is much louder.
Although our trouble shooting is different, outcome is positive. I enjoyed your video even though my radios are larger and more complicated as i align and cal mostly the R388 thru R-391 Collins. Thanks for what you do. Very informative
You’re the best Terry, you continue to remind me of my buddy and mentor George Runyan WB6YEC you also can fix anything and a real diagnostic and trouble shooter. Also a fellow AMer 3870Khz..73’s and Thank You! -.. . .- .- -.... .... -.- -.-
I think this is the best vid you have done, Terry. Excellent stuff! I really like the way you showed the logical process of troubleshooting the various problems this amp had. Thanks so much for sharing it!! Cheers, Simon
diceman220 man , I also had one not quite as old that I lost when a tornado hit our town,,,,, I really miss that sweet sounding amp! I'm not a terribly religious man but I've been on my knees many nights thanking God no one in my family was hurt
Very useful video you are really educating us on the realities of Tube amp Diagnosis. I had a nice old Scope, but sold it. Now i wish i had it back so i could see the sound wave. Thank You, Dennis
When I replaced my friends OT on his Bassman so we could use different cabinets with different resistance, I fired it up, and it was that one time I didn’t bother connecting a dummy load and scope. Nah, I went straight to the speaker. That’s the first and last time I’ll ever do that. The level of feedback coming through the amp was insane. Made me jump. In your video, I could hear that tone coming through the dummy load and knew that’s what it was immediately. It’s a familiar and traumatic sound for me, ahah haha haha.
I repaired an amp that always had a pleasant volume to it. Turns out the OT had a slight short on the primary that caused it to attenuate the volume kind of like the "Cerrem's mod". After I rewound the transformer I hooked it up and just casually did the old Pete Townsend windmill chord strike. I swear the amp was 5x as loud nearly blew my pants off and scared the crap out of me!
Thanks',Terry,great video!Nice watching you trouble-shoot live! Really interesting.It is obvious that you have seen some of these problems' before! : )
I just want to say I have learned much from D-lab and Uncle Doug. I think I noticed you didn't have a good connection when checking the filter caps at 5:00 with the test leads. Good video, I'm just happy I spotted something or maybe I didn't but still had an idea that was generated from all your great videos...
As always love to watch your videos Terry. I like the way you cruise thru the circuit, as to say, fun...I have a Tek 922 scope that I converted to a curve tracer, a la Mr. Carlson's Lab. I love that little scope too, BTW. Gary
I always add some series resistance in the filament chain to lower that voltage to 6.3 volts on my vintage amps. It also reduces surge current at start up. If you have ever watched Mr. Carlson's Lab video about how much current those filaments draw at start up. It is almost 2 amps per 12AX7 tube lot of stress on that power transformer.
I was lucky enough to get the feedback loop wired up backwards on both of my custom builds. Man does it ever make a squeal if you have a speaker hooked up.
Terry , thanks for posting ....my interest in building a 6v6 push pull is gaining interest. You dogwood videos and generally you make it fun Alberta Dave
As much as I love the 2 kHz sine wave test tone. You should have your guitar buddy record some riffs on some recording medium preferably a looping pedal So us guitar players can hear What these amps sound like.
Thanks for an awesome video! Maybe you could have a guitar with an open tuning and then just strum the open strings for a few times? We would love to hear what these beautiful amps sound like.
@@daleburrell6273 No but you can try!(D-Lab does a great job) A successful RU-vid channel IS an attempt to please everybody as measured by the number of subscribers. I humbly offered a suggestion. Love this channel even built a D-lab designed 6f6 amplifier from an old Regency police radio. Sounds great wide open through a Marshal 4x12 cab.
Just a comment about those green/yellow jumper leads. I’ve had issues in the past ‘cause they’re usually just crimped clips to thin stranded copper (usually through the vinyl insulation). Some don’t make contact, so always a good idea to peel back the insulation on the clips and solder them (then you don’t have to worry about a possible bad connection there).
Terry this was an excellent video as ever, can't help thinking if you had hit the red vino at the start you may have solved it even faster! Loving your work though and great to see a true live master in action! Off for a vino myself now. Cheers Paul in the UK
Regarding modern wall voltage. I used a 12v center tapped transformer as a bucking transformer to create vintage voltages. It can give me line voltage, and then I can switch it to go be me either ~110vac (tweed era voltage) or ~117vac (blackface era voltage) depending on what the wall is giving.
Great hands-on troubleshooting! Thanks to You and M.Caldeira I've revived two radios with cap issues. However, I was accompanied by a couple of beers and a cat, do You think I should move up to red wine and a dog before having a go at my guitaramps? Keep up the good work Terry! Cheers from Sweden!
If it utilizes negative feedback and the output transformer was replaced, the leads of the output transformer are reversed. Just flip the wires on the primary. What you had with the wrong transformer connections was a positive feedback circuit which is another name for an oscillator. And sure enough you had a square wave oscillator.
I was guestimating your next statement on the oscillation..rev polarity or out of phase audio xfrmr...great work.. The ole gray sponge here still can recall somethings..hihi. ..about my antique tube portable am radio.. 110 vac or 10 eveready 9 v . heirloom from 2 gens back..care to go thru it and swap the buzz for music?
Terry, just stumbled on your video! Great stuff, and it’s appreciated. Here’s a great question for you, if you please .. How do you calculate your charge for such a repair? Gracias!
399 volts at idle while normal for push pull Princetons, is way too high for tweed Princetons in my experience.Also too much filtering may seem okay technically but it changes the tone character of these amps,making them feel/sound tighter which in a way is not bad but just different sounding than the original circuit with less filtering.Also, spec sheets for 5y3 rectifier tube has 32uF as maximum allowed capacitance.Now there are two paralled 22uF caps giving around 44uf combined capacitance for the 5y3.
I did a google on 'Fender Princeton Mods' and a quick scan it appears a couple of those items you found different than the print lined up with one or more mods. Might be a good giggle if you do your own google knowing what's in that amp.
Terry is a really enjoyable video. Hey tried to donate to your channel but hit a wall when I hit the donate button. Could you confirm it's working. I'm hoping the issue isn't the Canadian money LOL.
The "hot" AC input line should really go to the switch first, then the fuse holder. Much safer in case someone pulls the fuse to check it. If the power switch is in the off position there is no voltage going to the fuse. The other way, if the fuse holder has the AC line to it first then the switch, someone could get a nasty shock. Much safer to wire hot line to switch first. I'm surprised this wasn't done that way.
I know this is an older video but could you tell me what the difference between the 5f1 circuit and the 5f2 are. Thank you love your videos big fan thank you.
Only $40 for parts.....But shipping from Hawaii had to cost a lot! I tell my customers that I automatically change out ALL old electrolytic caps because you fix it and then next week it breaks again and they blame you. Most Fender amps get played and thrown around hard.
Did you check or replace the 10K resistor after it had 200+ volts across it ? I know you cut power pretty fast but 200+ volts across a 10K resistor, means that 1/2 or 1 watt resistor was handling over 4 watts for a short time. E squared over R = Power. Nice fix by the way.
Metal Oxide resistors have small vent holes on the ends as far as I remember and handle surges much better. The 1-watt metal oxide resistors are about the same size as the old carbon resistors. Aren't the metal oxide resistors usually blue in color ? (his wasn't)
To check the current through the cathode resistor, just measure the voltage across the resistor and divide it by the resistor value. I = V/R. That's your current. No need to stick a current meter in line with the cathode resistor.
WONDERING about the three wire connection? I used your method of wiring till I saw the Hot Lead being wired to the On/Off Switch and then Back to the Fuse. I heard that if wired as I have always wired that if the amp goes down and the fuse isnt blown someone may try to change the fuse and get zapped if the amp is still plugged into power, What are your thoughts?
