Hoffman 3 tube reverb ?

[Madison]

Got it put together.
All voltages look good.
Rechecked resistor values.

When I turn up the mix on this it really kills the output.
When I turn the mix up all the way the output suffer severely, like maybe 25% of what it was.
Is this the way it supposed to work?

I am just running it unto the input of another amp.
When I roll the mix back to zero the amp sounds normal.

[eleventeen]

That northeast terminal on the "mix" pot labeled "6"......you got that going somewhere? Unless you do, as you turn the pot towards that end, you'll be getting a whole lot of nothing.

That "6" lug has to go to the cold side of the .1 uf cap coming from the rightmost 12AX7. If that wire is missing....

If that wire is present, that section of the 12AX7 (the 1-2-3 side) isn't working.

[sluckey]

Here's a schematic for that layout. Might come in handy while troubleshooting.

EDIT... Fixed schematic error.

[Madison]

That northeast terminal on the "mix" pot labeled "6"......you got that going somewhere? Unless you do, as you turn the pot towards that end, you'll be getting a whole lot of nothing.

That "6" lug has to go to the cold side of the .1 uf cap coming from the rightmost 12AX7. If that wire is missing....

If that wire is present, that section of the 12AX7 (the 1-2-3 side) isn't working.

#6 attached.

I'll check that triode again.
It almost acts like triode after the tank isn't working, if that's even possible.

Thanks for the schematic!

[PRR]

> When I turn the mix up all the way the output suffer severely

What are you going into? A guitar amp instrument input or something else?

[Madison]

> When I turn the mix up all the way the output suffer severely

What are you going into? A guitar amp instrument input or something else?

Guitar combo amp.
Have to lift the ground to get it quiet.

[Madison]

Getting closer.

That last triode V-3 pin 2.
I am only at 70VDC.
the chart calls for 116.

Actually everything on my build is about 20 volts over so I think I am something like 66 volts low there.
Hmmm why?
Tried a different tube.No go.

[Madison]

Increased the voltage. Strapped a resistor across the 2.2 M.
No go.

[sluckey]

That last triode V-3 pin 2.
I am only at 70VDC.
the chart calls for 116.

The voltage on pin 2 should be half the voltage on pin 1. If not, then maybe your 2.2MΩ resistors on the grid ain't right.

But, you need to be looking at the other half of V3 and the reverb driver circuit. You said...

When I roll the mix back to zero the amp sounds normal.

According to that statement, the cathode follower is working OK.

Just for info, this circuit is the same as the 6G15 except the driver circuit resembles that of an AB763. The V3 recovery and cathode follower and mixer is identical to a 6G15 and should play fine into the instrument input of a guitar amp.
 

[Madison]

Thanks Steve.

I have the typical reverb trans.  25K/8Ω

Just noticing my reverb tank.
Belton BMN3AB3C1B
Input:10Ω
Output:2250Ω

No good?

[Madison]

Working!
Not sure exactly what happened.
Messing with the tank wiring and it sounds fine.
Maybe because I have the tank and transformer out on the bench and some wires were crossed?

I'll see if I can get it together without any more troubles.

[Willabe]

Working!

 

Messing with the tank wiring and it sounds fine.
Maybe because I have the tank and transformer out on the bench and some wires were crossed?

Bad verb cables, verb jacks/cold solder joint, in to the out and out to the in between the chassis and verb tank, verb tank has bad wire to/from the little transformers that drive the springs?


            
                         Brad          

[Madison]

Spoke too soon.
It WAS working.
Played it for a few minutes.Sounded great.
Moved some stuff and now the SOS.
More searching to do.
Grrrrrr

BTW, anybody know what the voltage is supposed to be coming off V-2 pins 1/6-blue wire ?
I read like 329VDC

Working!

 

Messing with the tank wiring and it sounds fine.
Maybe because I have the tank and transformer out on the bench and some wires were crossed?

Bad verb cables, verb jacks/cold solder joint, in to the out and out to the in between the chassis and verb tank, verb tank has bad wire to/from the little transformers that drive the springs?


           
                         Brad           

Tried different wires to the tank.
Tried a different tank.
Thanks

[Madison]

Well.
The ONLY way I can seem to make it work is to bypass the 250p cap from the tone pot.
Even then the mix really doesn't work as a mix, it works more like a weird pan.

If I bypass the reverb pan and just hook the two RCA jacks together it the mix pot, etc./ circuit works.

Calling it a day.
Any more ideas welcome.
Thanks.

[sluckey]

Post some hi rez pics.

[Willabe]

Well.
The ONLY way I can seem to make it work is to bypass the 250p cap from the tone pot.
Even then the mix really doesn't work as a mix, it works more like a weird pan.

I think I'd try disconnecting the mix pot wiper from the output jack and lift the end of the 250pF cap that feeds the mix pot then jumper it to the output jack. Just to see if you get full wet signal to the amp.

I think that 250pF cap and or the mix pot be bad bad or they are wired wrong.

If I bypass the reverb pan and just hook the two RCA jacks together it the mix pot, etc./ circuit works.

That seems odd, wouldn't a 10 ohm signal from the verb Tx secondary load down the verb recovery tubes grid to nothing?



                      Brad      

[Willabe]

Here's a schematic for that layout.

Sluckey, your schematic is missing the .05 blocking cap on the dry/mix CF grid.

Edit; This part was for the younger/newer guys;

Without it there's dcv (Fender drawing shows 120dcv although the input 1M grid leak would then be in parallel with the CF 2.2M grid leak so it would be less then 120dcv?) on the guitar cables jack tip and input tubes grid. Between input tube pin 7 and the junction of the 2 @ 2.2M's that go to pin 2 of the CF.    



                           Brad    

[sluckey]

Sluckey, your schematic is missing the .05 blocking cap on the dry/mix CF grid.

yep