New TMB w/reverb Build

[foreverstrung]

I've built many speaker cabinets for amp heads with tolex and grill cloth. I am a carpenter and have been for over 40 years. I can certainly make cabinet for this amp, it's just finding the time. I own and run a construction company AND I'm raising my 3 grandchildren solo. Age 10, 8 and 7.....Time is what I don't have. What little I have, I choose "hopefully" wisely. After this discussion tho, I do believe I'll consider building one.

Any thoughts on this reverb issue? I played today and noticed that even at 2-3 on the knob, I can hear the reverb underneath the harshness. Turn it all the way to 9 and I hear only reverb, but it's not a good reverb. Light high pitch hiss when turning the knob too. On the PCB board I followed the line from the cap to the tube socket. Caps and resistors are as they should be. Has anyone else experienced this?

[Bieworm]

I've built many speaker cabinets for amp heads with tolex and grill cloth. I am a carpenter and have been for over 40 years. I can certainly make cabinet for this amp, it's just finding the time. I own and run a construction company AND I'm raising my 3 grandchildren solo. Age 10, 8 and 7.....Time is what I don't have. What little I have, I choose "hopefully" wisely. After this discussion tho, I do believe I'll consider building one.

Any thoughts on this reverb issue? I played today and noticed that even at 2-3 on the knob, I can hear the reverb underneath the harshness. Turn it all the way to 9 and I hear only reverb, but it's not a good reverb. Light high pitch hiss when turning the knob too. On the PCB board I followed the line from the cap to the tube socket. Caps and resistors are as they should be. Has anyone else experienced this?

Did you already try swapping the rca cable connectors between the jack inputs?
The schematic says in and out, but in means the return from the tank output and out is to the tank input. In colors, your red tulip should go in the 'in' on the amp.. that will go to the grid of the recovery circuit (pin 7)

[foreverstrung]

Did you already try swapping the rca cable connectors between the jack inputs?
The schematic says in and out, but in means the return from the tank output and out is to the tank input. In colors, your red tulip should go in the 'in' on the amp.. that will go to the grid of the recovery circuit (pin 7)

Yes. Reversing the RCA cables was the first thing I did. When I swapped them, there was no response from the Reverb pot at all. 1-10, no change whatsoever in the sound.
The other way, as I described, is harsh with reverb barely audible in the background until the pot is all the way up and then it's straight reverb, but not a sweet, wet reverb. Not a "good" reverb

[Bieworm]

Did you already try swapping the rca cable connectors between the jack inputs?
The schematic says in and out, but in means the return from the tank output and out is to the tank input. In colors, your red tulip should go in the 'in' on the amp.. that will go to the grid of the recovery circuit (pin 7)

Yes. Reversing the RCA cables was the first thing I did. When I swapped them, there was no response from the Reverb pot at all. 1-10, no change whatsoever in the sound.
The other way, as I described, is harsh with reverb barely audible in the background until the pot is all the way up and then it's straight reverb, but not a sweet, wet reverb. Not a "good" reverb

What pan do you have connected to the amp?

[foreverstrung]

What pan do you have connected to the amp?

By pan, do you mean my actual reverb spring ensemble? It's the one that came with the original components. After playing the amp more and kinda breaking it in, with the reverb now, 1-3 sounds good and 9-10. 4-8 is no bueno. Might be this reverb unit itself.

On another note, this cabinet I got from Tube Depot I can make work if I could just get the mirror image of this chassis plate. Any suggestions? If I could get the writing on the back side of the plate, it would be fine. The pots should be left to right, but I could make right to left work. Assuming the writing can get flipped. The way it's laid out, I don't think I can really get it into any combo amp. I could make this chassis work for a head, but not a combo. Any combo, the writing is still upside down and left to right pots.
Unless I'm missing something.
I'm not totally opposed to a head.

[JMPGuitars]

The reverb problem could be a parasitic oscillation causing that issue. Post a demo of what it sounds in each volume range.

Your scope might come in handy if that's the case.

I just checked, I only have head faceplates right now. Unfortunately, my laser isn't big enough to make you one (it would be in two pieces, which is kinda weird). I can order the combo version of the faceplate, but one-offs are expensive. I was planning on ordering a few faceplates soon, so if you're not in a rush, that would work out better.

Thanks,
Josh

[foreverstrung]

I just checked, I only have head faceplates right now. Unfortunately, my laser isn't big enough to make you one (it would be in two pieces, which is kinda weird). I can order the combo version of the faceplate, but one-offs are expensive. I was planning on ordering a few faceplates soon, so if you're not in a rush, that would work out better.

That would be great josh. No rush

[JMPGuitars]

That would be great josh. No rush

BTW- if you decide you would be okay with making a head version instead, I use their "Tall 20" British style head, but same thing, 10" depth for an 8" chassis.

[foreverstrung]

Update.
Still haven't taken care of the reverb issue. I'll upload a sound demo of it later today. Put the scope on it soon.
I've been fooling around with this amp all week and I'm very very happy with the sound. Very much looking fwd to adding the reverb.
I'm going to go ahead and build a head cabinet. Lots of great videos out there. I pulled out a couple old speaker cabinets I built about 6-7 years ago. They work, but man, my grill cloth work is awful. Tolex not bad. All of it has lots of room for improvement. My memory of these is twisted. LOL. I thought they were much nicer.
So I'll keep this thread updated with these items, but I'm also looking at my next project. Just throwing around some ideas. I really am being drawn to just something like an original 18w. On the download page, there's a few. I don't want all the bells and whistles. Just a vintage scheme that's relatively quiet.
As always, appreciate you alls thoughts

[Bieworm]

Not an 18w, but a 6G3 is a really great amp for overdrive. It was so much fun I even built a 35W 6L6 version of it.
The recent 18W Tremolo TMB I built has also reverb. I’m not a fan of the 1tube reverb. I won’t build it in an amp anymore. I’m glad I added the fx loop to use my reverb tanks with this otherwise great amp. But it’s personal preference.
I can’t seem to get it (1tube reverb) noise free either… in any amp I built. There’s always some low pitch noise when mix pot is past 50%.. like white noise, but darker in tone
FWIW all my blackface type reverbs are absolutely noise free

[JMPGuitars]

I really am being drawn to just something like an original 18w. On the download page, there's a few. I don't want all the bells and whistles. Just a vintage scheme that's relatively quiet.
As always, appreciate you alls thoughts

If you want a basic (but better) 18W, look at the 18W Modern Classics in the downloads section.

I can’t seem to get it (1tube reverb) noise free either… in any amp I built. There’s always some low pitch noise when mix pot is past 50%.. like white noise, but darker in tone
FWIW all my blackface type reverbs are absolutely noise free

I've never had an amp that had 100% noiseless reverb (fender, marshall, mesa, etc...). The 1 tube reverb isn't noiseless, but I haven't found it to be that noisy either.

Here's some of my earlier amps with reverb / gain cranked:

https://www.youtube.com/watch?v=EB0gux3Wrdk
https://www.youtube.com/watch?v=c2kVir5erwM

Both of those are cranked, and one is an EF86 preamp before I redesigned that preamp for lower noise/better gain.

Here's one of my most recent builds, a Tremolo TMB Reverb: https://www.youtube.com/watch?v=7NLzAzifDKg

I wouldn't accuse that of being noisy either.

Thanks,
Josh

[Bieworm]

You know, the noise isn’t that bad. In a band situation it’s not a bothering thing. And at home I don’t turn the reverb up to that level. It’s just not my cup of tea… I’m probably pickier than most when it comes to reverb.

[JMPGuitars]

You know, the noise isn’t that bad. In a band situation it’s not a bothering thing. And at home I don’t turn the reverb up to that level. It’s just not my cup of tea… I’m probably pickier than most when it comes to reverb.

That's fair. So here's your challenge then: make a standard 2-valve reverb in a Tremolo TMB. I was planning to eventually, but won't likely any time soon.

[Bieworm]

You know, the noise isn’t that bad. In a band situation it’s not a bothering thing. And at home I don’t turn the reverb up to that level. It’s just not my cup of tea… I’m probably pickier than most when it comes to reverb.

That's fair. So here's your challenge then: make a standard 2-valve reverb in a Tremolo TMB. I was planning to eventually, but won't likely any time soon.

Planning that… but I will first look at this one. Maybe I will add a tube or maybe I will do the recovery with mosfets

[foreverstrung]

https://youtu.be/50sEk-FK4l4
You can hear the reverb channel sounds like crap. Noisey. Little to no actual "reverb".
Like I said, I haven't spent a lot of time chasing this down. I've swapped out the RCA cables. And then back. Changed out the 12AX7. I did flip it over and stare at it for a while. LOL. Looking for the obvious.
Besides the reverb, this amp is quiet quiet.

[JMPGuitars]

https://youtu.be/50sEk-FK4l4
You can hear the reverb channel sounds like crap. Noisey. Little to no actual "reverb".
Like I said, I haven't spent a lot of time chasing this down. I've swapped out the RCA cables. And then back. Changed out the 12AX7. I did flip it over and stare at it for a while. LOL. Looking for the obvious.
Besides the reverb, this amp is quiet quiet.

It sounds like you have a wiring issue. You also need to double check and make sure the 221K resistor to ground on the red reverb jack is good. With the amp powered off, you can try measuring the resistance of V3 pin 7 to ground to test that.

Also make sure the jacks are tight...without breaking that 221K resistor.

Then break out the highlighter and do just the reverb section again.
Side note: instead of assuming the wiring is fine because you checked 3 times already, assume something IS wrong, and be pleasantly surprised if it isn't. Either way, search carefully for whatever is sneaking past you.

[foreverstrung]

So I swapped out my Siglent scope for a 1104x-e. I'm getting ready to fire it up for the first time and trying to get motivated. I've watched tons of videos on scopes but still really don't have a line on what I'm doing. I'd sure appreciate some very basic 1-2-3 direction for setting the unit up correctly and then chasing down the circuits. Like your explaining to a child, because I feel about as smart as one right now with this thing. I know the black wire with the 3 prongs plugs into the wall, but that's about it. lol
Josh mentioned to use a guitar in place of a signal generator a while back? Do I need that sound ever present?
TIA

[JMPGuitars]

So I swapped out my Siglent scope for a 1104x-e. I'm getting ready to fire it up for the first time and trying to get motivated. I've watched tons of videos on scopes but still really don't have a line on what I'm doing. I'd sure appreciate some very basic 1-2-3 direction for setting the unit up correctly and then chasing down the circuits. Like your explaining to a child, because I feel about as smart as one right now with this thing. I know the black wire with the 3 prongs plugs into the wall, but that's about it. lol
Josh mentioned to use a guitar in place of a signal generator a while back? Do I need that sound ever present?
TIA

A signal generator is required. To really test, you need a 1kHz sine wave being fed into the amp. This is the cheapest/decent signal generator I've used: https://www.newark.com/tenma/72-505/han ... dp/66F3575 (though I have a couple nicer ones I don't need anymore if you feel like wasting money ).

You can also get a signal generator app on your phone, but that's trickier to calibrate sometimes. Look for the "function generator" app.

Follow the directions to calibrate your scope probes. You'll be connecting the probe(s) to the calibration terminal on the scope. Press the "auto" button, and it will show you a square waveform. Adjust the screw on the probe as per the directions.

After you've calibrated your probes, leave them set to 10x. Then connect them directly to your signal generator, and set the generator for a 1kHz sine wave. Adjust the output of the signal generator to somewhere between 150 to 300mV (millivolts). That's a relative range for guitar, low mV being lower output pickups. You'll need to hit that "auto" button again to acquire your signal (at least until you get good at messing with the knobs).

Once the signal generator is calibrated to the correct range, you can then plug it into your amp's input jack.

Doing this test with the scope is much easier (and safer for your ears) with a "dummy load." Personally, I use an attenuator on my workbench as my dummy load (it has a speaker cone in it). Alternatively, you can google making a dummy load yourself with a high-wattage 16ohm or 8ohm resistor. NEVER turn your amp on without a speaker or dummy load connected.

This page has some great info on using an oscilloscope for an audio amp: http://www.r-type.org/articles/art-125.htm

You can start by connecting the scope probe to your speaker jack. Chances are, that may look normal if you're just troubleshooting your reverb. So you will need to look at the schematic and what points bring audio signal into, through, and out of the reverb circuit.

Thanks,
Josh

[foreverstrung]

A signal generator is required. To really test, you need a 1kHz sine wave being fed into the amp. This is the cheapest/decent signal generator I've used: https://www.newark.com/tenma/72-505/han ... dp/66F3575 (though I have a couple nicer ones I don't need anymore if you feel like wasting money ).

This link is a dead end. I'm interested in what you've got laying around and how much. I'd like something reliable, but cost effective too.
I'd also like to see the cheap one you recommended if you can find a diff link for it.

Follow the directions to calibrate your scope probes. You'll be connecting the probe(s) to the calibration terminal on the scope. Press the "auto" button, and it will show you a square waveform. Adjust the screw on the probe as per the directions.

After you've calibrated your probes, leave them set to 10x. Then connect them directly to your signal generator, and set the generator for a 1kHz sine wave. Adjust the output of the signal generator to somewhere between 150 to 300mV (millivolts). That's a relative range for guitar, low mV being lower output pickups. You'll need to hit that "auto" button again to acquire your signal (at least until you get good at messing with the knobs).

Once the signal generator is calibrated to the correct range, you can then plug it into your amp's input jack.

Doing this test with the scope is much easier (and safer for your ears) with a "dummy load." Personally, I use an attenuator on my workbench as my dummy load (it has a speaker cone in it). Alternatively, you can google making a dummy load yourself with a high-wattage 16ohm or 8ohm resistor. NEVER turn your amp on without a speaker or dummy load connected.

This page has some great info on using an oscilloscope for an audio amp: http://www.r-type.org/articles/art-125.htm



You can start by connecting the scope probe to your speaker jack. Chances are, that may look normal if you're just troubleshooting your reverb. So you will need to look at the schematic and what points bring audio signal into, through, and out of the reverb circuit.

Thx for all of that.
I've watched some good videos using a scope on a vacuum tube amp. It's interesting, but slow. I am realizing that I do need to let all of it soak in.

It sounds like you have a wiring issue. You also need to double check and make sure the 221K resistor to ground on the red reverb jack is good. With the amp powered off, you can try measuring the resistance of V3 pin 7 to ground to test that.

Also make sure the jacks are tight...without breaking that 221K resistor.

Pin 7 on V3 reads 221k, so that resistor appears good. I'm going to pull the PCB board again and check that everything looks good on the underside of the RCA connectors. Measuring off the PCB board, all the caps and resistors, inline with the reverb channel, are reading as there suppose to.
I haven't found anything grounding out. I'll keep looking.

This is what I picked up for a dummy load
https://www.amazon.com/gp/product/B0002 ... UTF8&psc=1

In Gerald Webars book, Tube amp talk..., he's got a chapter on building a dummy load with a speaker. What you suggested made me think of it. This resistor I listed above looks like it'll work too.

[JMPGuitars]

I clicked the link above, and it appears to work, but try clicking here instead.

That dummy load should be fine, make sure to set the amp to 8 ohms.

Be very careful disassembling your amp over and over again.

The cheap signal generator linked above is fine. The biggest benefit of the others I have is that you can enter the exact amplitude without having to guess or test every time. They can also do lots of other things, but for this test all you need is a 1kHz sine wave. Email me if you want more details on the fancier signal generators.

Thanks,
Josh