Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: BrianS on April 16, 2020, 12:14:27 pm

Title: figuring out a replacement reverb tank.
Post by: BrianS on April 16, 2020, 12:14:27 pm

Hello all,
So I've got a pretty rare Ampeg amp on my bench...a 1967 Reverberocket III.  This is one of the "golden glo" series.  Here's the schematic from Doug's stash: https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_reverbrocket3.pdf (https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_reverbrocket3.pdf)
The output of the tank measures as open and I'm not seeing any bad connections inside.  I've fixed quite a few tanks with broken lead wires, but I'm not seeing this in this one...it all looks good, but measures open.
The input resistance that I'm measuring is 167 ohms, and there are a few tanks out there with 150 ohm input impedances, which I'm hoping will be a close enough match.

What kind of math should I be doing to figure out what the output impedance of the tank should be?

The is one of the weirdest amps I've worked on....
Brian

Title: Re: figuring out a replacement reverb tank.
Post by: sluckey on April 16, 2020, 12:48:55 pm

No math. The input ***RESISTANCE*** of 167Ω corresponds to an input ***IMPEDANCE*** of 1475Ω. So, you need a 4FB type tank for that amp. Look at this pdf to complete the type number.

Title: Re: figuring out a replacement reverb tank.
Post by: Latole on April 16, 2020, 12:51:42 pm

https://amprepairparts.com/reverbdcchart.htm

Look F in the screen copy

By the way I google Reverb Rocket reverb tank !

Title: Re: figuring out a replacement reverb tank.
Post by: 2deaf on April 16, 2020, 12:58:01 pm

The first letter after the first number needs to be "F" on modern tanks.  The second letter needs to be "B".

A quick look through AES shows three available:  4FB3A1B, 4FB3A1A, and 9FB2A1C.

If your amp has the tank mounted on the side panel, none of them are spec'ed for that.  But any one of the three will work, nonetheless.  The 9F one is for vertical mount and it is theoretically the best for end mount if you buy into that sort of thing.

The Gibbs/Hammond "C" tank has both input and output sleeve connectors connected to the tank housing.  All three of the above are also configured like this.     

Title: Re: figuring out a replacement reverb tank.
Post by: BrianS on April 16, 2020, 12:58:49 pm

Thank you.  Thanks for the links and pics.  I understand the difference between impedance and resistance, just didn't realize there would be that big a difference between the two in this instance.  Although I also had no good reason to believe they would be similar either...

Brian

Title: Re: figuring out a replacement reverb tank.
Post by: Latole on April 16, 2020, 01:01:24 pm

Impedance and resistance are two different world, both in ohms .....