Reverb on T1-RVT

Hello everyone! I just bough my first piece of Guild gear, a T1-RVT with the 12/8 inch speaker config., reverb, and tremolo. I wont wear you out with how much I love my new amp, but I do have a question. The reverb has not worked at all since I bought the amp, and the tremolo was only coming out through the 12". At first, nothing was coming out through the 8" speaker, but after I replaced a microphonic preamp tube the tremolo now comes out through both speakers. I have the original foot switch, and when I engage the reverb, nothing happens except when I dime the reverb, and then the 8" emits a little hiss. Before I swapped the tubes, the smaller speaker would howl when the reverb was switched on. I don't know much about this amp. Are both speakers supposed to function all the time, or just when the effects are turned on? Is the 8" ever supposed to work with the tremolo, or was it originally only for the reverb? Do you think that this amp has been rewired? I know that there are very knowledgeable people here who can help, and I thank you for looking at this post. Once I figure out how to upload photos I will.

Pic posting thread.

If you thump the side of the amp with your hand, do you hear the springs crashing together?
You replaced the reverb tube with the proper 6bm8?

Someone who has one should be along presently....

I have to run out for a bit, and I'll give it a thump and double check the tube later. I'm hesitant to turn the amp on too much because it's still got the old two pronger waiting to kill someone. Thanks for the reply, I do appreciate it.

Yeah, that needs to go.

I plugged the amp in and turned the reverb on (without the guitar connected) and the reverb made a very loud hum, although without the reverb on the amp is surprisingly quiet. I thumped the amp on all sides and also tapped the reverb tank itself, and there wasn't any noise whatsoever. The investigation shall continue. Anybody out there experienced this phenomenon? Thanks again!

No advice, just best wishes - the guys what know will help you out.

I had no reverb because I had no reverb speaker(s), and I'm just getting them rebuilt for a T1-RVT and a Thunderbird.

Hope you also have such a simple solution.

Hi Norton Nice and welcome to LTG. Always tough troubleshooting by post reply but let's give a shot. This is a fragment of the amp's schematic; the magenta arrows are the directions the signal is travelling. The red line is the feed from the preamp during normal (and trem) function to the reverb amp's output tube and speaker. The signal bypasses the preamp (green box) of the reverb amp at the bottom and is fed to the front 1/2 of the 6BM8 which acts like a gain stage or preamp, through the pentode (power) 1/2 of the 6BM8, through the output transformer, and to the speaker. For our purposes, the fact that the speaker puts out normal and trem signals means the 6BM8, OT, and speaker are working.

The reverb signal is taken from the 12" speaker - magenta arrow at right -and fed to the reverb can (blue box), and then to the 12AX7 reverb preamp tube, then the 6BM8 and so on. You'll notice the blue arrow to the reverb control. If your reverb isn't working but the rest of the reverb amp processes a dry signal, then the problem is between the 12" speaker and the input of the 6BM8.



You need to get contact cleaner, both types; general and lubricating. The signal from the 12" speaker goes into the reverb can usually with an RCA connection; take the can out and with the general contact cleaner, clean the male and female reverb-in and reverb-out connections at the can; spray them and push on / pull off several times. If your amp has hardwired connections (no jacks/plugs) you can forget this.

At the reverb amp, take the 12AX7 and 6BM8 out and clean the pins and sockets with the general cleaner; same thing, get them wet, in and out a few times. Remember to gently wiggle side-to-side as you tug to break up any corrosion. Anyway, in/out 4 or 5 times. Reverb control; you'll have to take the chassis out but you have to clean the reverb and the other control pots with lubricating-type contact cleaner; get them wet and spin them back and forth several times. Finally, open the footswitch, soak the little switch bodies with lubricating-type contact cleaner and operate the buttons several times.

I strongly suggest you do all of this because even if you fix the problem by short-cutting, doing this stuff will keep all the headaches they can cause from coming back and biting you. Make sure your rabbit's foot is in plain view and fire up. No go? Try subbing in a known-good 12AX7 in the reverb amp. If none of this works, then chances are either one/the other/ both transducers in the reverb can are shot or one of the resistors or capacitors on the reverb amp circuit board has gone off the reservation. If the former, you can get a new can; if the latter, then intervention will be necessary.

Good luck with your amp! CJ

Thank you so much! I really appreciate you going out of your way to help me with this. I am going to pick up some contact cleaner while I'm out today and follow these instructions.

Your schematic and explanations are extremely helpful, especially since this is the first amp I will ever work on. In upgrading my guitar, I've unleashed my inner tone freak, and now that I have landed an amp with tone that I love, I can't wait to get said amp to it's full potential.

I really do appreciate the assistance from everyone; this is the best forum I have ever seen!

I'll update this post after further investigation.

Take care! ---- Norton

Hi NN: happy to help. Make sure you get both types of contact cleaner; lubricating and non-lubricating. The non-lubricating type isn't any good for controls - they need a little film of oil and the non-lubricating type can thin the dab of grease that's on the bearing in the shaft of the pot. The things can last a lifetime if cared for.

If you get it running correctly and if it hasn't been done yet, the amp will need a 3-wire power cord. If you don't want to fool with it and lots of people don't, it isn't that big a deal to have a tech do it but it is important.

Good luck! CJ

An additional word to john kidder--NEVER run a tube amp without a proper load on the circuit...running the amp without a speaker can seriously damage the output stage, most particularly the output transformer and potentially the output tube.

People used to solidstate amps often make this mistake. A lower impedance load on a solid state amp is a no-no, but a higher impedance load on a tube amp (particularly an open circuit) is a no-no.

+1

count_scrofula said:

An additional word to john kidder--NEVER run a tube amp without a proper load on the circuit...running the amp without a speaker can seriously damage the output stage, most particularly the output transformer and potentially the output tube.

Click to expand...

Thanks Count, and great to hear from you again.
The Cap'n guided me firmly and diplomatically through a slightly risky approach to seeing if my reverb output transformers were fried (well, diplomatically except that he insists on calling such things "cowboying" - as an old cowhand I do feel a little slighted and need to keep repeating the proper verb for things that might work but might not but we'll just go ahead with it anyway is actually "farmered", not "cowboyed"), all the while admonishing me never to run a tube amp without a load. Thanks to him, not to me, the speakers were always in line, just non-functional.

Luckily both amps seem to have survived the malfunctioning speakers withput (apparent) damage elsewhere. The Tbird's up and running (although it seems to have less reverb effect that I expected, further decoding and following this thread may assist), and I'l get the rebuilt 8" for the T1RVT this afternoon and see how she goes.

john_kidder said:

[quote="count_scrofula":11omrisx]An additional word to john kidder--NEVER run a tube amp without a proper load on the circuit...running the amp without a speaker can seriously damage the output stage, most particularly the output transformer and potentially the output tube.

Click to expand...

Thanks Count, and great to hear from you again. The Cap'n guided me firmly and diplomatically ... except that he insists on calling such things "cowboying" - as an old cowhand I do feel a little slighted and need to keep repeating the proper verb for things that might work but might not but we'll just go ahead with it anyway is actually "farmered", not "cowboyed") ... [/quote:11omrisx] Hi John; my father's people were farmers going back several generations. He and his admired cowboys for their self-reliance, committment to the care of their charges, and their simple pleasures of sleeping out on the prairie under the stars breaking wind. The term is intended to convey a willingness to measure and accept risk. I'm glad the amp is working but even more pleased that we don't have to troubleshoot the reverb power supply, pc board, and OT via post and reply! J

Would you rather be "sheepboying" instead?

<shudder>

!

Veer on, Columbia, veer on. I'm watching Bound for Glory, about Woody Guthrie, as I type. Time for some new Woody and Cisco and even the just-departed Utah Phillips to remind us that folk are everywhere troubled and oppressed by the rich and powerful, and that folk song is about just that. Damn.

Cowboying: I once had a boss who asked me to carry out a task that would have provided a false impression to some potential investors. Our little company desperately needed the money, as little tech companies do. But I told my friend and boss that I wouldn't do it because it was unethical and I didn't work that way. He said scornfully "Hell, Kidder, I thought you were a cowboy." I said that I was indeed a cowboy, or at least that I had been, and that what cowboys actually did, all myth aside, was take care of cows and grass. We were just husbandmen, I said, not wild and crazy shoot-em-ups and rebels. So now I just joke around about it when someone says "he sure cowboyed that thing" or something similar - I don't actually take any offense, of course.

And Cap'n, you're completely right - the single most important thing I learned from those years in cow camps and big country was self-reliance. The second most important thing I learned was that farmers work harder and longer for less reward than anyone else I've ever met. Three times I've had the great good luck when hiring junior engineers to find young guys who grew up on a farm - you juist know they'll make do with what's at hand, that they won't quit till it's done, and that they'll step in anywhere without prompting when they see that something needs to be done. I use "farmered" as a joke too.

But sheepherding, Default, now that's a different matter altogether. I do mention to people when they talk about those "cowboys" on Brokeback Mountain that that was a sheep camp, not a cow camp, and of course everyone knows about sheep camps. And that stupid joke aside, the few open range sheepherders I've met (very few - 2 in BC and 3 in Montana) have to be about the toughest sob's I've ever run into. That's no job for a wimp.

40% of the surface of the earth has grazing animals on it, and they all have underpaid overworked camel-yak-goat-cow-sheep-buffalo herders to tend them. There's a strong kinship among us pastoralists, all over the world a common language, and an instant understanding known only among them that's been there.

Back to amps now - my Thunderbird has a reverb signal, the footswitch works, all is cool, except that the effect is less than I believe it should be. I have done the steps John outlined for the T1RVT - clean all connections, tubes, etc. - might have been an improvement at the margin, but not at all pronounced. Is there any electrical measurement I can make to give me a sense of the output after the reverb transformer, and is there a benchmark against which to compare it? Or am I (once again) circling around the wrong issue altogether?

Didn't you hear about the farmer that won the lottery? They asked him what he was going to do with the winnings and he said "I'll keep farming until the money runs out."
I know what you mean, John. Both my parents came from farms and a lot of my skills and attitudes come directly from that type of life.


Ok, have you tried switching in a reverb can from one of your Thunder 1's? It could be the can in your Thunderbird is weak.

Re: !

john_kidder said:

... ... my Thunderbird has a reverb signal, the footswitch works ... the effect is less than I believe it should be ... done the steps ...Is there any electrical measurement I can make to give me a sense of the output after the reverb transformer, and is there a benchmark against which to compare it?

Click to expand...

Hi John; yes - determining power output of the reverb amp is possible but it requires calculating the 6BM8's plate dissipation, the speaker's db output, and other arcane statistics that are beyond my know-how. I will say that if it's never had its power supply filter and cathode caps replaced, there is almost no chance that it will perform as well as it was intended. Filter and cathode caps are to used amps what valve jobs and points / plugs / condensors are to used cars. Sitting right next to the reverb amp is the reverb multi-section capacitor; it supplies smoothed, filtered power to the 6BM8's plate, screen and triode section and power to both halves of the 12AX7. Even if the primary can cap were not replaced, that item alone will bring the reverb to life.

And .... as in the immortal words of PhillySteve, that filter cap will keep on filtering until the filter runs out ... :wink: CJ