What about the xfrmr in the standalone Reverb unit?

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11/30/1999 4:46 PM

PurpleP

What about the xfrmr in the standalone Reverb unit? The standalone reverb unit has the output of a 6K6   connected to the tranny which drives the tank.     How does the impedence of the 6K6 compare to the 12AT7? I am no EE, and am learning this stuff, so I do not know.     Would a different transformer need to be used? I am planning to build a reverb unit as my next project, and (perhaps naively) assumed the transformer would be the same as the "standard" ones used in Fenders.

 

11/30/1999 5:44 PM
Randall Aiken	I believe that one is rated at 7K primary impedance, which is about right for a 6K6. Anything from around 6K to 9K would probably be fine.     Randall Aiken

 

11/30/1999 6:16 PM

Doc

The transformer for a driver circuit using a power pentode is a small single ended output transformer. The reverb tank input coil on a typical fender reverb unit is about 8 ohms. So you need a transformer capable of about 3 watts that will satisfy the plate load requirements of the tube when driving an 8ohm load. A 6K6 likes a higher load than the 6V6, by about a factor of 2. You could, for instance, get satisfactory results using a small Champ output transformer (which is wound for a 6V6 into a 4ohm load) for a reverb driver circuit utilizing a 6K6 into an 8ohm reverb tank.     The load matching isn't that critical, because the reverb tank will saturate at a little over 1 watt input. A load on the tube that is not optimum for maximum power transfer will still allow plenty of power to be extracted to drive the reverb tank.     I never measured the turns ratio on either the original 6G15 reverb unit (6K6) or the reissue (supplied with a 6V6 from the factory). I don't know if the transformers are wound in the same ratio, or closer to optimum for the particular tube supplied. I do run my RI reverb unit with a 6K6 and it sounds fine to me. Bruce keeps good notes on the many transformers he's encountered over the years. Maybe he's measured some of these in stand alone reverb units.     The reverb transformer for a 12AT7 combo reverb is not really suitable for use with a 6V6, 6K6, 6AQ5, or 6BQ5 driver. A replacement part for the 6G15 can be obtained, but really any universal output transformer like those from Hammond can be used. Even a reclaimed output transformer from a table radio would work. Those things are usually 2.5k/ 3.2 ohms, so would end up as 5k into 8ohms.

 

11/30/1999 6:47 PM
PurpleP	Thanks much..this is great information!   Thanks for your insight, guys. I am glad I asked...especially since the usual Fender xfrmr will not do the trick.

 

11/30/1999 11:23 PM
Dirk	Angela has the Fender part for the reissue available for $14. At least that was the price a few months ago.     I measured one, and the primary is a little over 6k ohms with an 8 ohm load on the secondary.

 

12/1/1999 12:04 AM
John Stokes	It has been suggested that one of the "shortcomings" of the reissue reverb is that this tranny is a cheezy part (relatively speaking), and that the sound can be improved by subbing in a better quality transformer. I think I recall reading that someone swapped in a tranny they got from Kendrick and they claimed it helped. Anyone here try this?

 

12/1/1999 1:15 AM
Dirk	I haven't built mine into the circuit yet, but it my first impression when I took it out of the box was that it was really tiny. Bell cover to bell cover measures 1 5/8, the laminations are 1 5/8 x 1 1/4 x just under 1/2" thick.     Certainly could have more beef.

 

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