Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: John on February 02, 2015, 01:29:14 pm

Title: Reverb question
Post by: John on February 02, 2015, 01:29:14 pm

Hi fellas, I'm building another amp for a buddy of mine. He wants spring reverb, not digital. I'll be using Doug's reverb tranny and Tubenit's 1-tube reverb. It's another SE build using 6SL7s if that matters.


My question is, Bruce (my buddy) is buying a 9" tank from Accutronics; we're limited on space or I'd just use Doug's tank. ANYWAY. Do I want the tank with the high impedance output? I looked at the tranny specs and it says secondary: 14.5K and so I would think I'd want the 12K tank. But, as this is my virginal trip into spring reverb, I thought I'd best ask. Below is the question he asked me.


"It is measured in ohms.  @ 1khz. Input range from 10 OHMS TO 1925 OHMS.
 OUTPUT RANGE FROM 600 OHMS TO 12000 OHMS."

Thank you all!

Title: Re: Reverb question
Post by: sluckey on February 02, 2015, 01:44:40 pm

Quote

I looked at the tranny specs and it says secondary: 14.5K

Doug's reverb transformer has a PRIMARY impedance of 14.5K. The SECONDARY impedance is 4Ω. You will need a tank with a low input impedance and high output impedance, such as 1AB2B1B or 8AB2A1B.

Title: Re: Reverb question
Post by: John on February 02, 2015, 04:11:30 pm

Argh. With what I miss and mis-read, it's a wonder I'm still alive! Thanks!

Title: Re: Reverb question
Post by: Willabe on February 02, 2015, 05:44:45 pm

 :laugh:    me too!

Title: Re: Reverb question
Post by: PRR on February 02, 2015, 06:08:51 pm

> tank with the high impedance output?

Asked like that: Yes. The Tank Output should be high Z for best hiss.

However as Sluckey spotted, your question is about Tank INput, which should be similar to RT Output (secondary), which is 4-10 Ohms. Anywhere in that area is fine; a 600 Ohm Tank INput will not get much drive from a Fender-type 15K:4 RT.

Title: Re: Reverb question
Post by: John on February 06, 2015, 07:23:41 am

Thanks again for the replies. Now, another question. I've googled and " heard it both ways. "  (Sean Spencer)


Is it okay to use the screen supply node to power the RT? Being this is a SE amp, will it have a much higher likelihood of hum? I typically use a 10 or 12K resistor at the power tube to get the screen voltage a little under the plate voltage, if that matters.


If I have to, I can squeeze another R/C filter in there, but if it's not necessary.....


I'm once again learning just how much I don't know.  :icon_biggrin:

Title: Re: Reverb question
Post by: sluckey on February 06, 2015, 07:46:48 am

Quote

Is it okay to use the screen supply node to power the RT?

Yes, Fender did.

Title: Re: Reverb question
Post by: John on February 06, 2015, 08:58:59 am

Thanks!