adding tube reverb to Hoffman Blues Jr

[squarhawk@charter.net]

I have built the Hoffman Blues Jr Kit and added a Princeton reverb circuit. I added a 12AT7 tube, reverb transformer and using the unused half of V2 for the reverb return. I had to remove the 470K resistor on the reverb pot to get the reverb to work. (Why did I have to remove that resistor?) My only problem now is when the reverb is set to it's lowest setting I lose virually all the volume on the amp. I'm no amp tech or engineer, I just did a lot of reading and used what little common sense I have. I'm looking for suggestions on where to tie the basic Fender reverb circuit into Dougs Blues Jr circuit. I keep the reverb on about 3 so everything sounds OK but something is amiss since I had to remove the resistor and I lose overall volume when reverb is set to 1. Any suggestions or comments? Thanks 

[sluckey]

We need to see a schematic that shows how you connected the PR reverb circuit to the BJ circuit.

That 470K is important in the PR circuit. It's used to mix the reverb with the dry signal. It also prevents the reverb pot from killing the dry signal. Put the 470K back in.

We need to see a schematic that shows how you connected the PR reverb circuit to the BJ circuit.

EDIT... You "may" improve the problem simply by swapping the wires on the wiper and hot side of the reverb pot.

[squarhawk@charter.net]

Thanks for the quick response. I'll draw something in the next day or so and post it. I've tried reinstalling the 470K resistor several times and it kills the reverb completely. I read on the forum that someone removed theirs to get theirs to work so I removed it and I got reverb. I see that most Fender circuits have a dry signal bypass made up of a 3.3M resistor and a 10 pF cap. I do not have that in my circuit. Everything works perfectly and sounds GREAT except when the reverb is on 1 which it never is so it's not really a problem. I'm just so close to having everything perfect I want to knock this last small issue out. I have attached the circuit I coppied. I built it on a seperate small board and mounted it on the back of the chasis

[sluckey]

Very easy to try this...

EDIT... You "may" improve the problem simply by swapping the wires on the wiper and hot side of the reverb pot.

[squarhawk@charter.net]

I am using a 100KL reverb pot where Doug has the meat pot. I replaced the meat pot with a switch which works fine. I have written in my connecttion point to the Blues Jr board on the reverb schhematic. This may not be legibe. Just need suggestions on where to tie the 3 wires of the revevb circuit to Dougs Blues Jr board.   Thanks, Stan

[sluckey]

Very easy to try this...

EDIT... You "may" improve the problem simply by swapping the wires on the wiper and hot side of the reverb pot.

The 100K plate resistor for the reverb recovery amp is connected wrong according to your note. It should connect to point "X" on Hoffman's schematic. I would probably connect the 470K from the reverb pot to the center lug of the treble pot.

[squarhawk@charter.net]

That's one idea I haven't tried. I'll give it a shot and report back. Either way I certainly appreciate you taking the time to look into it. I can change caps and ID and replace a bad resistor but that's about the extent of my knowledge. This is my first build and I have really enjoyed it and it's been very rewarding. Thank you Sir!

[squarhawk@charter.net]

Tried your suggestions to move the 100K plate resistor connection to point "X" and reinstalled the 470K resistor and moved that connection to the center treble lug. The result was NO reverb. I moved the X point connection back to the cap off of V2 and still no reverb. Removed the 470K but left that connection on the treble lug and and now have reverb that does not kill the amp volume when the reverb is set to 1. Everything seems to work correctly now and I'm sastisfied with it as is but if there is something fundalmentally wrong I'm open to changing things around. It's all a learning experience for me. I do lose a little, but not much, overall volume when I connect the reveb circuit but that may be normal. It is still loud for a 15 watt amp. I have a Greenback speaker. Thanks again for your suggestions and I'm open to other suggestions although I'm happy with it as is. Thanks again, Stan