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Reverb tanks on ebay for EMS Synthi and VCS3 - Beware !
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author Reverb tanks on ebay for EMS Synthi and VCS3 - Beware !
papz
https://www.befr.ebay.be/itm/232820638122?ViewItem=&item=232820638122

Seller is "littlepomponette" located in Canada.

These tanks have the right appearance but the DC resistances are not the ones expected in a Synthi or VCS3.
Input : 165 ohms instead of 1.8 ohms
Output : 190 ohms instead of 900 ohms

"8S" is stamped inside, the good ones are "8T".
The bad ones have black input coil and red output coil.
The good ones have red input coil and green output coil.
Scot Solida
What would be the effect of using the bad one? I bought one from this seller last year. The tank works, but there is a problem with the mix pot. However, I’m not sure if that’s a result of the tank or the pot.
papz
The result is a very weak reverb sound, especially noticeable in MK2 units.

The MK1 reverb circuit (with PA234 / GEL234F1) seems more tolerant to impedance and the effect is less blatant.

I have on the bench a Synthi AKS (MK2 with MFC6070 driver) whose tank was replaced by one of these and the reverb is very weak, I swapped the boards A with my AKS, which has a hybrid board A with MK1 reverb driver and output amps and MK2 PSU, to help locate the issue. With the hybrid board A, the wrong tank sounds much better although not perfect. With the other board A in my AKS the reverb sounds as it should.
Scot Solida
Thanks papz. No, the reverb isn’t weak on the one I bought for my MkII. There is just some odd behaviour when turning the Mix pot - but I assumed it was a bad pot.
papz
With the wrong tank, wet depth and amplitude are very weak but the mix pot behavior is normal, same as with a good tank.

I think your VCS3 is a MK2, if your reverb is not weak with this tank, it probably has the good impedances. Maybe the seller had both 8S and 8T types ?
Scot Solida
That may be... and it was quite a while ago. I seem to remember it saying 8T inside. We’ll pop it open and have a look when we get a chance. However, as I said, the signal is strong, so I think I got a good tank.
sanders
I also have one of the eBay tanks; I got it at least two two years ago. I'd have to open it up to determine which version it is, but I'm curious now.

My only problem with the Reverb is a tremendous amount of noise and feedback, and I've used two different driver circuits now. The signal itself became much clearer and stronger after I replaced my original MFC6070 with one of Papz 741 daughter boards.

I used commercial RCA stereo speaker cables to connect to the Reverb Tank, and I'm wondering if there's a better method?
papz
You can measure the DC resistance on the tank's solder pads, no need to take it apart.
The cables to and from the tank should be shielded and the shielding connected to ground.
Pierrelegere
wow, thanks!
papz
I informed the seller via ebay, he seems to ignore my message. confused
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