Reverb advice needed

[rfgordon]

OK, I got the harp amp w/ reverb circuit fired up tonight, and it works. I need to tweak the tone control some and replace a defective noval socket, but that's just chowder.

I used the reverb circuit posted below. This amp is very simple:

1. Parallel triodes run at low voltage into a vol/tone combo, then thru the resistor to feed the reverb circuit.
2. Reverb per the posted schematic. I used a 1 Meg pot instead of a 2 Meg pot for the verb control.
3. The PI is the self-balancing paraphase inverter a la 5D5, so I can run a symmetry control on it to control feedback.
4. Pair 6L6 cathode bias.

Here's the issue: the reverb is extremely weak. Is that the nature of this verb design, or are there changes I can make to bump it up a bit? The takeoff resistor here is 100k, I think I used 220k, and Fenders run something like 3M3 ohms. How does changing this resistor affect the depth of the verb?

I look forward to y'all sharing your reverb secrets of the ancient ninja with me.
Thanks

[mhuss]

The series signal resistor (R1 in your diagram) seems way small; these are normally at least 470k and often as high as 2M2. Making this larger will reduce the 'dry' signal.

--mark

[rfgordon]

I've tweaked a bunch of things, but I'm beginning to suspect the reverb transformer. Why? Because I have a 100k plate resistor "upstream" of it, and 325VDC before the 100k, but only like 8 VDC after it, and almost nothing on the plate of that 12AX7. Also, there's no voltage on the cathode for that half of the 12AX7.

Help!!

[rfgordon]

Well boys and girls, it was, as I suspected from the start, a bad reverb xfrmr. I got a Heyboer from Mojo and stuck it in there, and SHAZAM! Reverb!!

So now I have this killer harp amp with reverb. I don't have a harp, but I dug out my cheeziest Radio Shack omni mic and plugged in. I hooted and howled into the mic, turning up to get feedback (which was pretty easy with this mic). I then turned the symmetry control (from Gerald Weber's book), and, lo and behold, you get to a point where the feedback just disappears! Way cool. I could crank this amp almost all the way up and point the mic at the speaker and get no feedback. A harp player's dream. I am so stoked. Now, if he'll just come across with the cash for the cab, speaker and tubes.......

[jimipage]

hey, Rich, this reverb circuit looks interesting. I'm getting ready to build my first amp w/reverb and I'd like to know more about what you've done with this.
My first question: what is the value of R10? (ohms/watts)
next: how does this circuit sound(is the signal strong enough) being driven by only a paralleled 12A_7?
and: what tubes are represented in this circuit? Is the first tube in this circuit paralled?
and one more: do you think this would work with a typical LTP driver?

thanks!

[rfgordon]

jimipage,
I think I put a 10k on R10, but I don't remember. As for the strength of the amp, it's not as loud as most guitar amps, but the guy can just about dime it in most of the clubs he plays. Since there's no gain/mixer stage after the verb, the reverb only gets really deep when the volume is cranked. I liked the overall vibe of the amp, so it inspired me to make the one I just started.

In the new amp I have a parallel 12AX7 into tweed style vol/tone, then a straight-up blackface reverb circuit, then mixer/gain stage into a long-tail PI, then two 6L6 in cathode bias. Sort of tweed-meets-blackface thing. It'll drive a 15" Weber Chicago speaker (which is killer, BTW).

I don't have the ability to put the schematics in the computer, but if you PM me your snail mail address, I can mail you copies of the Echo-Harp and the new one I'm calling the Longneck. I'm gonna put a bottle opener on the front. Very roadhouse.