ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Input impedance for cap-coupled "Ampeg" style rev tanks


 
7/19/2004 2:08 AM
Rob Mercure
email
Input impedance for cap-coupled "Ampeg" style rev tanks
Folks,  
 
I know I've got it "somewhere" in my notes but does anyone know "off the top of their head" what the input impedance is/was for the "Ampeg/Gibson" style capacitively coupled reverb tanks. My recollection is around 2K or so but I'll be damned if I can find my notes. My 1976 Ampeg service manual lists all of these units as "4C."  
 
Thanks  
 
Rob
 
7/19/2004 7:04 AM
Dr._Photon
email

a type 4C (Hammond organ style) has a 1.5K (~200 ohms DC) impedance. These are the 4 spring (looks like two) long tanks similar to Fender's save the impedance.
 
 
  Friday
Book Of The Day The Ultimate Tone, Volume III by Kevin O'Connor
Have you ever wondered if there is a better way to build a Bassman, Champ, Plexi, an 800, AC-30, Bulldog or Portaflex? Or you wanted to build an SVT with off-the-shelf parts? How about a master-volume amp that doesn’t change tone with the master setting? Everything you need to know is right here, including: proper grounding techniques, wiring methods, and mechanical considerations. Eighteen chapters cover the “iconic” amps everyone knows and loves, with schematics and layouts for each, along with the technical history of the product. Eyelet-board and chassis-mounted tube socket construction is used throughout, for easy servicing and modding. TUT3 is very accessible even if you cannot fully read a schematic and is a "must have" if you are going to build an amp for your self.

Note: The Ampage Archive is an Amazon Associate site. A small commission is paid to the site owner on any qualified purchase made after clicking an associate link such as the one above.
 
7/19/2004 4:52 PM
Ray Ivers
email

Rob,  
 
The highest input Z I can find for an Accutronics tank is 1925 ohms, corresponding to an 'F' as the second designator (e.g. 4FB3A??, which would be a 4-spring pan with 1925 ohms input Z, 500 ohms output Z, long delay, and grounded input & output. Some Ampegs have a wire-form lock (2nd-to-last digit = 3) or no lock (1), and there are six pan orientations so I can't really help you with the last digit without more info.  
 
Ray
 
7/19/2004 5:02 PM
Mark Lavelle
email
Re: Input impedance for cap-coupled "Ampeg" style rev ta
quote:
"The highest input Z I can find for an Accutronics tank is 1925 ohms, corresponding to an 'F' as the second designator"
That's what I used in my Gemini I...
 
7/19/2004 6:19 PM
Rob Mercure
email

Ray, Mark, Dr.P, thanks for the responses. What I'm dong is "back-assward" engineering (wouldn't honor it with "reverse" engineering). A customer has an old Music Man 2275-130 and has asked me to see what it would take to convert it into an all tube amp. The existing pan is a 4FB3A3B Accutronics and I was trying to determine if I could adequately drive it with an Ampeg cap coupled type circuit - from Mark's reply it seems that this should work. A few years ago when I was creating my various "reverbs from hell" designs I crafted several cap coupled circuits that I really loved - by far my favorite reverb circuits.  
 
Loud clean amps aren't in much demand so I was thinking about eliminating the voltage doubler B+ circuit which would give me a 255 VAC secondary to rectify - switching to 6V6s from the existing 6CA7s should give me lotsa extra heater current so I was going to propose a single channel 40W-ish amp with reverb and lotsa transformer reserve - but you could still get almost 100W out of 6L6GCs at these voltages so I may consider switching options. He's already spent a few dollars with me on a 1964 Vibroverb "rebuild" and a YSB-1A and Magnatone "overhauls" so I can't "tap him out" too much :).  
 
Rob
 
7/20/2004 7:33 PM
Jack Koochin
email

Hi Rob!  
I'm still scratching my head about a JC-120 reverb problem, have no schematic, and was wondering if you could help. The DC resistance of the reverb tank (O.C. Electronics tank) output transducer is about 200 ohms, and the input transducer is about 1 ohm. I thought Ahaa!! ... burnt out transducer, but then I checked this against my Bandmaster tank, and it's about the same reading on both transducers... 1 ohm DC??  
Anyhow, as you might've read in my other thread, the JC-120 reverb works, but puts out a distorted signal. The Bandmaster reverb works fine.  
Jack
 
7/21/2004 7:10 AM
Carl Gigun
email

Here's a chart for normal resistance of reverb tanks relative to their AC impedance. http://www.accutronicsreverb.com/ioic.htm  
 
-Carl Gigun
 
   Page 1 of 2 Next> Last Page>>