A Very Unusual Tube Amp Problem......and Repair 

Thanks, 2R :)

I love the clarity of his videos, too, but I prefer the Jazz to the Precision..

You're welcome, Jason :)

I hope they are pleasant ones, Tim. You're welcome.

Thanks, Jim, for joining us and for posting a nice comment.

+Audio Tech Labs You're welcome, ATL :)

+Finom1 You're welcome, F1.....glad you enjoyed the video :)

+kardRatzinger Thanks, Kard. I understand there are several other meanings for the term, but I think you can see why it's particularly appropriate in this case :)

Absolutely. Usually when I hear motorboating of an amp, it reminds me of a thumper. Sounds a lot like my Yamaha SR400 idling.

You're welcome, Wayne. We appreciate it :)

+Dave Bogusky Thanks, Dave, and regards to Igloo :)

Thanks, Ed. It's always good to hear from you.

+saturn5tony You're welcome, Tony....glad you liked it.

You're welcome, Kevin. Thanks for your nice comments. We will do our best :)

+Haroslav Drastic Like death and taxes, Haroslav, Rusty and I are here to stay :)

Thank heavens you were up to watch it, Vinny. Thanks for the nice comments :)

+Harrison Hein That's good news, Harrison.....keep up the good work. Old amps need love too :)

Will do

You're welcome, John. I figure there is nothing to lose, so I root around looking for the broken lead and am sometimes able to find it.....but not always :)

That's great to hear, Miguel. Congratulations on your scratch-building success. We will :)

@@UncleDoug Had a question for you, If I'm using a PT with 120mA HV secondary. Do I need to use a filter choke thats rated for 120mA? or does the filter choke only need to be rated for the current your actually drawing from that secondary? I have a 100mA filter choke I want to use but the PT secondary is rated at 120mA. Would it blow the filter choke?

Thanks, Vince :)

+Ken Davis You're welcome, Ken, and best regards to Tater :)

+Buddy Martin You're welcome, Buddy. The trick is to find the other end of the broken lead. Most of the time, I can, and if so then it's generally fairly easy (not on the eyes) to mend the break. Once repaired, the OPT is generally as good as new.

+Marvio Botticelli You're welcome, Marvio. It looks like the student has progressed beyond the teacher :) Rusty and I are glad the videos were helpful. Thanks for watching.

Thanks, David :)

+StonyRC Thanks, Stony. Now, if I could only get PAID like a vascular surgeon, Rusty's (and my) menu would definitely improve :)

You're welcome, Lefty.

It's always a good way to begin any conversation :)

+toxicgraphix You're welcome, TG, and thanks for your very nice comments. Rusty and I really appreciate it :)

You're welcome. Thanks for the nice comments.

+Cameron Walker Thanks, Cameron. It's good to be back. Hopefully, some vintage rock amps will show up for sale or repair. If they do, I will definitely feature them in videos.....so stay tuned :)

You're welcome, DT.....glad you liked it :)

+Randy Schartiger Thanks, Randy.....glad you liked it. Regards to Q-Ball :)

+Joop S You're welcome, JS :)

Thanks so much, Joel. It took many years to perfect "the tap" and I'm glad someone out there appreciates it :)

+Paul Passat You're welcome, Paul. I have heard it before, when working on radios, but have never encountered the problem with a guitar or PA amp. It generally "putts" at a faster rate, but the sound is unmistakable.

Thanks, VonZ :)

If it weren't for Rusty's guidance, I would just be an old hack :)

Thanks. Glad you enjoyed it :)

+Cawfee Dawg Thanks, CD. It's good to be back :)

+John Cunningham Thanks, John. I've never seen it before in a guitar amp, and it's good to know that I'm not alone. It now seems to perform and behave quite well, so the problem appears to be fixed.

+John Miner Thanks, John. Rusty and I appreciate the nice comments.

Thanks, Michael.

You're welcome, ZB :)

Thanks, Chad :)

+SiliconSet Thanks, SS. I guess he always thinks that way :)

You're welcome, Nik :)

You're welcome, Thomas.

+Bret H I agree with your analysis, Bret. Thanks for watching and commenting :)

+su pyrow Thanks, SP :)

You got it good buddy! 73!

+Greg's Garage Thanks, Greg :)

+Greg's Garage Hey Greg! Cool to see you here.

I love this channel... Sometimes you'll see me post as SkyScraper Guitars too!!! UD &R rock.

Thanks, Greg. Rusty and I have come to really like and appreciate our viewers....like you. What a great extended family we all belong to :)

***** Hey Sceaming deal, Yes, very nice . I'm just outside Willamina, so not to far from Lincoln City. I've seen some nice day's at LC. Will take the winter's for the summer's. Thanks for commenting. Be good, C.

+Cass Virgillo Hey fellow Oregonian! The weather was perfect here in Portland today. Good day for beers, music, and top it all of with a super cool Uncle Doug video. What could be better?

BrianOfAteionas Hey Brian, I couldn't agree more. Happy 1st. Uncle Doug is my favorite channel. I'm getting part's together to build a Fender 5F1 Champ as seen in his 2 part video series. Take care, C.

+Cass Virgillo It looks like you Northwesterner's are having a nice chat. Thanks for all the nice comments.....Rusty and I really appreciate hearing from you all.

Uncle Doug Hi Uncle Doug, I've never had so many reply's to one comment. Be good, C.

+Barefeet200 Thanks, BF :)

+The Guitologist Thanks, Brad. Yes, they are very well-made, attractive, compact, and functional. I would say they are one of the best candidates I can think of for guitar conversion.....and, as you said, one of only two brands I can think of from Texas :)

Thanks, Ross. One of my favorite "de-animalizations" was the removal of a putrid rat's nest, constructed mainly of tin foil, from the chassis of a really nice early tweed Gretsch amp......I shudder to think about the "light show" that might have occurred if I had simply plugged it in, as-is.

Thanks, Tony.

Thanks, Tim :)

+Barnekkid Analog meters can perform tasks that digital meters cannot. They are both very valuable and useful tools. By all means, dust it off and begin using it, BK. You will wonder how you ever did without it :)

It's our pleasure to share them with you, CC.

Thanks, Aaron.

That's good to hear, GM :)

+aperioguitar Thanks, AG :)

+otteronbass You're welcome, Otter.

Thanks, BiG........glad you enjoyed it. We do tend to lose that which we cease to use.

You're welcome, Mike. Sadly, Rusty passed away several years ago, but I'm sure he would have appreciated your kindness.

Uncle Doug Im sorry to hear this Uncle Doug, he looked like such a nice boy. I love our dogs like children, sometimes I think even more because my dogs don’t disrespect me, lol. All the wonderful creatures need is love, food, water and a warm bed and they are totally content and give back love in such great magnitude. Keep up the great work with your very helpful videos, you have furthered my knowledge considerably, and for this I thank you sir, God bless 🙂❤️

Greetings, Zane. That's great to hear. Best of luck with your new career :)

+charlie brown We will, Charlie......and Rusty says "hi" to you all.

+redfishbum Thanks, Bart :)

+August Lyons Thanks, August....we will :)

+Is1amization by Immigration Thanks, I by I. I too initially suspected a filter cap as the likely culprit.

You're welcome, Troy, and congratulations on a successful repair of your amp. That was a close call on the plate current. I shudder to think what your plate dissipation was at 96mA for each output tube. To reduce your gain and mellow things out a little, you might try experimenting by substituting lower gain duo-triodes (12AT7, 12AU7, 12AY7, etc.) for one of the 12AX7's in your pre-amp.

Ahhh, I was under the impression that my power tubes were burning so hot due to the failing Bridge rectifier that was in the amp originally. After installing a new one that is beefed-up according to the specifications I assumed that was the reason why the voltage changed on my power tubes. 45 milliamps is maximum for my amplifier readjusting the bias after replacing the bridge rectifier has put the amplifier back in correct operating condition. I am an automotive technician by trade so I do understand alternating current and direct current. I am slowly learning the current flow in a guitar amplifier and why components do what they do.

Tubes overheat when the plate voltage and plate current within them is too high. This would not be the result of a failing rectifier or a new rectifier, but because the bias of the tubes is set incorrectly. Biasing involves more than simply adjusting the plate current. You should watch my video on biasing of double-ended amplifiers to see and understand the full process.

You're welcome, Jack. Good luck with your project.

Thanks, TA. Sarcasm is like aftershave lotion......a little can go a long way :) But when it's directed at objects and deeds, rather than specific individuals, I tend to like it too......as you can probably tell ;) The pets all say "Hi".

Thanks, John. Rusty and I appreciate the kind words :)

Thanks twice, Ricardo :)

+PAUL HAMMERSLEY You're welcome, Paul :)

Thanks, VC :)

+Michael Austin Thanks, Michael.

+Bobby Tectalabyss Thanks, Bobby, and best regards to Molly :)

Thanks, Ray :)

+Steve Dewitt Thanks, Steve :)

There are people out there who have forgotten more than I know, Tom.......but thanks !!

+Donald Filbert The diameter of a tranny coil wire only depends on the current flowing through at first glances. As being this one the wire of the primary coil the current through it is rather small.

+TubiCal Good answer, TC. Thanks.

+Ben Morris Thanks, Ben. In my case, it was caused by an open primary winding in the output transformer, but filter caps are a more common cause of the problem.....usually accompanied by a hum. Good luck with the repair.

Thanks, Doug. (When I get round to it)!

Thanks, JT :)

You're welcome, Ron :)

Thanks, Andrew. Rusty is a tough negotiator, but his agent is even worse.....we're still working on his new contract :)

+dennis walsh Thanks, Dennis, and congratulations on your successful (and money saving) surgery :)

It's hard not to, Peter. He's a very special guy :)

Thanks so much, Dwight. Likewise :)

Thanks, TH :)

Excellent advice, GB. Thanks for sharing it with us.

+Dennis Cochran Thanks, Dennis.

+Jim Lavespere Thanks, Jim. With so much rust, it must have been in a damp location....yet the wooden cabinet is in great shape. Very mysterious.

When you consider the size of the international audience, JT, I guess the presence of 11 slimy, belly-crawling, juvenile idiots isn't all that great a percentage :)

Me too, Henry. Thanks :)

Thanks, CM. So do I......they seem to occur when you are least ready to cope with them.

Greetings, Phil, and thanks for all the very nice comments. We're glad you found our channel and assure you that we've posted videos showing exactly the procedure you inquired about. Please see the one about cathode biasing.

@@UncleDoug Thanks Doug, I surely will. The reason this came up (checking cathode bias resistor) is I have a small combo amp, hand wired by a very small company in AZ called Red Plate (most people never heard of them). The amps are immaculately hand wired... My model (Black Loop model) has a Cathode bias and Keith from Red Plate (who built the amp) assures me I can put two 6V6 power tubes in the amp to replace the two 6L6 tubes. The one thing I must do (according to Keith with my cathode bias amp) is to turn the speaker ohm selector on the amp, from the current 8 ohm position, to 4 ohms to allow the 6V6 tubes to live in harmony with the amp. There's a lot more to his explanation why I can do this swap, with him also alluding that current 6V6 tubes are much more robust now and able to handle much higher voltages. (I am leaving quite a bit out as to Keith's explanation, but trying to be brief. His full explanation would give better context and details and glad to share it). Keith did also say however, that a 6L6 amp, (like my Red Plate amp), will sound better if using 6L6 tubes, as intended. So hence, I wanted to measure the cathode bias resistor before putting a pair of 6V6s in the amp (6V6s to only use for recording) and not live. Thanks. Phil NYC Area

@@uptownphotography Phil, I have no experience with Red Plate amps. Since the load resistance of 6V6's is higher than 6L6's it seems strange that you switch to a lower impedance (4 Ohm) for the 6V6's.....watch my video on the Impedance Ratio to see why. However, if the guy who built the amp says to do that, then he probably knows what's best for the circuit. I personally don't understand the desire to replace the 6L6's with 6V6's......it seems like taking a risk for no real benefit......but best of luck.

@@UncleDoug Basically, I want to do the swap to get the amp to break up and overdrive at lower sound levels (more like a Fender Princeton would do) so that when recording at my home studio, I don't bring the house down and disturb other people in the house. Hope that makes sense, but I totally get your point. Maybe, I'll just buy a smaller 6V6 tube amp for recording (hopefully that does not cost too much) and just use that for recording. Budget is a concern right now until I am working a full schedule again with my photography (The virus impacted it badly)....Thanks all The Best. Phil

@@uptownphotography Sorry to hear of your business setbacks, UP.....I hope things improve for you. The difference in breakup volume won't be all that great, I'm afraid. Have you considered investing in an attenuator? They aren't cheap, but they are very effective. Good luck.

Thanks, Mike. Glad you like it :)

You are welcome good sir. You and Rusty please keep delivering true Craftsmanship.

We shall, as long as we have encouragement from nice viewers, like you :)