6G15 Reverb Unit Pre-Build Questions

[Wombaticus]

Update: I finally had some time last weekend to finish wiring this reverb unit up. By the time I finished building a light bulb limiter for initial power-up, and measuring the B+ without tubes it was very late, so I did not have much time to mess with it. After seeing good voltages at the bridge rectifier, I threw in the tubes, connected the tank, and hooked it up to my buddies 2-stroke amp we recently built.

It does not appear to be working however. When on it passes the guitar signal through to the amp, but there is no reverb. The mix, dwell, and tone knobs do not seem to affect the sound very much. I do not have a foot switch yet, but I was under the assumption that the unit would be permanently on without it.

I need to go back through and take voltage measurements to get a better idea of what is going on, but my main question is...... isn't it a good sign that it is at least passing the guitar signal through to the amp, even if clean? I'm thinking it should be something simple that I can (fingers-crossed) fix easily.

It's always a good sign when an amp is passing audio. But in the case of the 6G15 it doesn't help you a whole hell of a lot, since the dry signal path is very very simple, just a single triode, then out - and the wet side makes up about 85% of the circuitry of the amp.

With the power off and the caps discharged, I would print out the schematic, and trace the circuit with a highlighter, checking continuity as you go to confirm that you've actually built what you think you've built and that there aren't any missing or inappropriate connections or something inadvertently shunting the signal to ground.

Only then would I fire it up again for complete voltage measurements. Then, when you're satisfied that the voltages are all approximately correct, you can probably work backwards with your multimeter to see where audio continuity to the output is lost... for instance, if you're probing the grid (one hand behind your back remember!) of the reverb recovery triode, and you hear a "pop" when you contact the grid, then you have continuity from that point forward.

[Wittgenstein]

That's what I was thinking.. thanks for the suggestions. I will make sure to go back through and re-check it again before firing it up.

Here is my understanding of this reverb unit: (please correct me if I am wrong)

The "wet" signal gets amplified by the first half of the 12AT7 who's plate connects to the second half of the 12AT7's grid (controls dwell and re-boosts signal). This half connects (via plate to grid) to the 6V6 which boost the signal to match the pan's impedance. The signal then returns from the pan and runs through one half of the 12AX7 who's plate controls the tone, and finally to output.

The "dry" signal runs from the input through a 0.047pf cap, to the other half of the 12AX7, and out through the cathode to the output.

So all that I can be sure of, is that the "dry" signal path is working.

[52 Bill]

You are correct in your signal path description. So far you know that half of the output tube is working and the power supply is working as well.

If you shake the reverb tank does it make noise through the output? If it does then the reverb recovery stage is working. If not, then that's where you start to look for problems.

Work backwards through the wet side until you find out where the signal stops.

[Wittgenstein]

It's Alive!

I had some time last night to poke around inside this reverb unit. I started as usual (even though the bleeder resistors knock it down to almost nothing) by draining the caps. I then double checked all my connections against the schematic while checking for continuity. Everything checked out, so I fired it back up with the tubes in to take some voltages. I was surprised to see no voltages anywhere in the circuit.... lol. The power transformer was obviously working, putting 250VAC or so on the secondaries and 6.3V to heaters (tubes were glowing like they should), but the "+" side of the bridge rectifier did not show any DC voltage. After waiting a few minutes for the iron to heat up, I re-flowed and added a bit of solder to the turrets the rectifier connects to, and gave it another shot.....

Fired it up and it sounds amazing!!!! There is almost no hum from the reverb unit. What little there is I suspect is from this terrible cable that I am using. I have new cables on the way. I then went through with the multimeter comparing my voltages to those written on Fender's schematic. All my voltages are the the same as what is written plus 14 Volts give or take a volt or two. So for example it shows 300V at the first filter cap and 295V at the second, where mine runs at 314V (first cap) and 310V (second cap) and so on. I would assume this is normal as my wall voltage is 121VAC vs roughly 110VAC back in the day.

The only thing that I noticed that I was curious about, was how microphonic the tubes are. Is this normal in this unit or did I just get some noisy tubes? The 6V6 and especially the 12AT7 are very audible when I tap on them. I figure it will not matter too much, as it will be in a separate cab sitting on the floor anyways. Once again, any suggestions, criticisms, or comments are welcome.

[tubeswell]

Have you tried swapping those tubes?

[Wittgenstein]

Have you tried swapping those tubes?

I have not. I think I might have a used old 12AT7 from a lot of tubes I purchased, but I need to buy another one. The AX7 is a wide base Sovtek which I wanted to try. I read it's less monophonic and fits the reverb unit well. Any thoughts on just using a new EH 12AX7 vs the wide base? I have a few new 6V6's that I can try, and I'm waiting for my buddy to drop off an old 6K6.

[Wittgenstein]

It was too late to play very loud last night when I tried it out, but I will mess around with it more tonight. I have only played it through my buddies Princeton/Dave Hunter 2-Stroke amp, but I really want to hear it through my Champ and Deluxe. I'm also considering buying the 3 spring pan (~$20) to see if I like the sound more.

I will try an upload some sound clips in the near future. For now, I'm just using a Shure 57 and two condenser mics into my Tascam M-164UF interface.

[kurtdaniel]

waiting for the sound clips!! nice build.. i wish i have a guitar how to know same as you do..

[Wittgenstein]

waiting for the sound clips!! nice build..

Sorry for the delay... here are 2 samples. It's my buddy playing his MIA Strat through both my reverb unit into my 5E3 Deluxe build for the wet signal, and my buddies Princeton (2 stroke build) for the dry, with a single Shure 57 mic between the two.

Sample 1

Sample 2

[tubeswell]

Sounds beyudefil!

[Wittgenstein]

I was really surprised by how much different the 6v6 sounds vs the 6K6 in this reverb unit. The 6K6 allows me to play with the dwell and tone more without it sounding bad or too washed out, but the 6V6 sounds better to me through my low wattage amps. When playing through my 5E3 the 6K6 is where it is at. I have a dovetail jig and my router set to the correct depth to make well fitting joints, but I have yet to cut into the beautiful boards to finish up this build. Lately I have been considering just buying a pre-made cabinet for my 5E3 Deluxe and calling it a day so I don't have so many unfinished projects going at once. Being my first build, I paid ~ $80 for a chassis so I know it will fit. Any suggestions on where I can get the cheapest tweed deluxe cab.

[tubeswell]

Any suggestions on where I can get the cheapest tweed deluxe cab.

https://taweber.powweb.com/store/wccabs.htm

[Wombaticus]

I was really surprised by how much different the 6v6 sounds vs the 6K6 in this reverb unit. The 6K6 allows me to play with the dwell and tone more without it sounding bad or too washed out, but the 6V6 sounds better to me through my low wattage amps. When playing through my 5E3 the 6K6 is where it is at. I have a dovetail jig and my router set to the correct depth to make well fitting joints, but I have yet to cut into the beautiful boards to finish up this build. Lately I have been considering just buying a pre-made cabinet for my 5E3 Deluxe and calling it a day so I don't have so many unfinished projects going at once. Being my first build, I paid ~ $80 for a chassis so I know it will fit. Any suggestions on where I can get the cheapest tweed deluxe cab.

For tweed-style cabs, I can give a very stong recommendation to Bruce Birling at Memphis amps. His are handbuilt for the price of mass-produced, and he is quite flexible if you need alterations to some dimensions, etc. For instance, I put my 6G15 into one of the 5E3 style head cabs, and had the opening at the top widened by a couple inches to accommodate my layout... No problem for Bruce.


Your clips sound just great, by the way. Rich beautiful clean tones!

[Wittgenstein]

For tweed-style cabs, I can give a very strong recommendation to Bruce Birling at Memphis amps. His are handbuilt for the price of mass-produced, and he is quite flexible if you need alterations to some dimensions, etc.

$195 shipped is the best price I have seen yet, thanks. Time to start saving.