How to tell different ohm taps in an output transformer?

[Satamax]

stokes,
I am finally in the process of identifying the load required by the speaker jacks in this Guild amp, as well as by two other amps (a 1472 and a 1482 Silvertones that have two separate taps on their output tranny).
I have also found the technique described here by you, satamax and enzo in the Gerald Weber's dvd, that definitely helped me to understand how the test is practically done.

Now I have a doubt about the plate impedance value of 6V6 and 6L6 tubes.
You mentioned 6600 ohms for a pair of 6V6 and 4500 ohms for a pair of 6L6.
I have found different values in my tube data sheets for class AB1 push-pull operation, that is:

- 8000 ohms for a pair of 6V6GT (General Electric datasheet, Duncan Amps TDSL datasheet);
- 5600 ohms for a pair of 6L6GC (Svetlana datasheet, Duncan Amps TDSL datasheet).

Which one is correct?

Hi Carlo, load on teh plates can varry, depending on the voltage, the power you're looking for, the distortion level you can cope with. Check here, you have three different plate loads for two different voltages. And you also have to remember often the guitar amps are using lowish plate loads. Plus normaly, you should plot your voltage, dissipation and all against the loadline. Trying to stay in the midle of the linear portion of it.

HTH.

Bye.

Max.

[stokes]

Carlo,I just got your message about this post.Max has pretty much hit the nail on the head with his response.The loads I quoted are about what Fender runs those tubes at.I quoted 6600 ohms for a pair of 6V6's,but I have indeed used trannies that read between 5000 and 8000 ohms with a pair of 6V6's with good results.With guitar amps,the ratings and such in the manuals dont necessarily pan out.You have a fairly wide range of usable values.Now I am not saying an OT with a 5000 ohm primary is going to sound the same as an 8000ohm primary,thats where experimentation comes in.Hope this helps.

[Rick Erickson]

How do I tell which one is the 8 ohm jack?

It would be the one that puts out maximum power into an 8 Ohm load. Just hook up the amp to an 8 Ohm dummy load, run a sine wave into it just up to the point of clipping and measure the voltage across the load. The whole point of "impedance matching" is to develop maximum power transfer from the source to the load.

RE