The Steel Guitar Forum

I recently purchased a used Amp from the forum. It was better than described when I received. When playing through it though, it sounded a bit grainy and the Reverb is way up in the mix.
I took it to a rehearsal and played at volume and the sound was slightly broken up and the reverb was way too much. I set the dial at less than 2.
Next day I checked and found the Reverb tube 12AT7 was DOA.
I swapped it for a 12AX7 I had from another amp and the sound cleaned up, but the reverb sucks.
Is there anything I can do to adjust the reverb, or does it need to go to a tech??
Patrick

If you don't have a good 12AT7, I'd get one and try that before anything else...

What Chris says! Although the tubes are similar, and both work in the socket, the internal gain of each tune is different. Hence the AT and AX designations.

If you search on 12AT7 and 12AX7 on the Forum, you will see the difference.

What Chris says! Although the tubes are similar, and both work in the socket, the internal gain of each tune is different. Hence the AT and AX designations.

If you search on 12AT7 and 12AX7 on the Forum, you will see the difference.

As mentioned already, 12AX7 is not a good tube to drive the reverb. Too much gain. Max use a 12AT7

I don't recall what I have there, but I find somewhere between 2 and 3 is all that I need. I think. I don't have any numbers, mine has chicken head knobs.

Thanks, I'll find a 12AT7 and put it there, but I'm surprised the reverb worked at all with the tube being doa?
Also, I like the long spring reverb, but the guitar signal is way washed out. I have an old Fender tube stand alone reverb, and it sounds like that but with the mix set to full wet.
I'll let you know how the tube swap does.
Patrick

I removed all the tubes, and found there was also a 12AX7 in V6 Reverb return socket.
I found some NOS 12AU7 tubes and installed them.
The guitar is way out in front and cleaner.
My ZB is in the middle of making new longer pedal rods, so I didn't get a chance to try it, but my Tele and Strat sound killer.
The reverb's still a bit big and dark toned, but the tube crunch is awesome with 6 string.
Not sure what the ZB will sound like??

Would a 12AT7 or 12AY7 brighten the reverb tone?
Is there a pot on the board that can be tweaked?

Thanks for the replies,
Patrick

If you only use one channel of the amp, you can route the reverb return to the other unused channel. That'll give you reverb eq

From right to left there should be a 12AT7 in the third slot and one just before the power tubes. The one before the power tubes has one stage working the reverb and the other stage pushing the power one last time before the signal hits the 6l6's. Use a 12AT7. I just ran into somewhat of the same problem with my twin and it cured it. All the other pre-amp tubes are 12AX7. 12 AU7 tubes are weaker than either one of the above mentioned tunes.

The tube before the power tubes is the phase inverter, has nothing to do with reverb. The reverb tubes are v3 and v4, with v3 being the 12AT7. Here are what the preamp tubes do, from right to left

V1- First gain stage channel 1
V2- First gain stage channel 2
V3- Reverb driver
V4- 2nd gain stage for channel 2 and reverb recovery
V5- Tremolo
V6- Phase inverter

Thanks for the clarification Howard.

Thanks all,
I realise the 12AU7 is rated about 20 on a 12AX7 scale of 100.
Those tubes made a big difference so that at least the amp is playable.
I will get some 12AT7 tubes and report back.
Patrick

Patrick - 12AT7 is not a good preamp tube because they are very noisy. I would try a 12AY7 or 5751 if you can find one. I know JJ makes them and they are inexpensive.

Welcome to the ZB club Patrick!

Installed the 12AT7 tubes and the shimmer is back and the amp sounds good. Reverb is still kinda big though.

Tim, I'm interested in your take on this particular amp. Would you please list out how you would tube this amp, including power tubes.

Dave, I'd been considering a more modern guitar with knee levers again, so after I heard you at Humbolt Hoedown, I ended up buying a '68 D-10 8x7 from Joe Goldmark.
Hatton and Jones did some magic to it and it plays sooo smooooth.
Patrick

My D-10 and S-10 ZBs get used a lot. Just picked up another S-10....

Regarding your reverb, you might have the reverb pan with three springs. If possible check it out and try to find the more common pan with two springs. I used to use the three spring version but found them a bit washy and went back to two springs......

Cheers!
Dave

Patrick, you might find this interesting

http://bb.steelguitarforum.com/viewtopi ... ight=12at7

Patrick Ickes wrote: Tim, I'm interested in your take on this particular amp. Would you please list out how you would tube this amp, including power tubes.

Tubes are only going to take you part of the way, unfortunately. Its no secret that I am not a huge fan of the wave soldered PCB re-issues. It might look like a Fender, but under the hood its no Fender.

Without beating a dead horse too much about hand wired, blah blah blah: if you are savvy with a soldering iron, you can try to mount a "Dwell" pot on the rear panel. This is basically a 1Megohm audio pot between pins 2+7 (which are in parallel on the driver side) and the 500p/1M junction coming off of channel 2. That way you can use a good old 12AT7 and control the signal feeding into the tank with the pot.

If you are trying to do it just by swapping tubes, you can try a 12DW7 in V4 (just to the left of the reverb transformer). This is a cool tube - one triode is similar to a 12AU7 (pins 1-3) and that would be on the reverb recovery side. The other half 6-8 is like a 12AX7 so the channel mixer and overall headroom of the amp should stay the same. JJ makes one which are about $10-15 new.

Thanks for all the replies!
I used the 2 12AT7 tubes in a gig Sunday and it worked good.
I'll experiment with the other tubes as suggested in the future.
I think I'll try and dampen those reverb springs. I have the Accutroncs series 9 w/3 long ass springs, so maybe that's the real culprit.
Patrick

You should seriously consider swapping out the Acutronic's reverb for a Mod brand. I did this in my Nashville 112 and there is no comparison, so much better than the stock reverb. And it only cost $19.95 plus 12.00 shipping from Tubes and More AKA Antique Electronics Supply in Mesa, AZ. The Mod is better built, too. Just make sure that you get the correct model as a replacement for what you have now.
'
If you are still unhappy with the reverb, and want to spend $179.00, then I highly recommend the Wet Reverb pedal. Smoothest reverb I have ever heard, even better than the Lexicon MPX-1 that I used to have with the John Hughey and Larry Sasser settings programmed in. .

The Reverb swap sounds interesting. As long as we are talking Custom Twins what are you guys using for settings? I am using a lacquer Williams.

dp

So I swapped tubes around and got a 2 long spring MOD reverb pan.
The amp is awesome with my Teles and Strat. Great string separation, punch, and compression when pushed a little. Reverb is big, but not washy.
My ZB sounds OK, but not great.
I guess that's the Blackface sound six stringers want and rave about, but not for my 10/10 strings.
I'll probably sell the amp.
I wanted to thank all of you for the help.
Patrick

Craig, I keep Bright off, bass nearly all the way up, mids around 6-8, and treble a bit lower. I find I cannot get a bad sound from mine