Can someone assist please - Paramount question

[Guy Boisvert]

If I decide in a month to change my 5670 tube, do I have to re-adjust the little blue trim pot for the new tube ?

Thank you


Guy

[johnsonad]

Yes

[Paul Birkeland]

For the 300B, it's entirely unlikely that you will need to readjust the tube.

The 5670 tubes tend to be absurdly consistent. 

[johnsonad]

In my experience with a dozen different brands and plate structures, you need to adjust it every time.  I wish my experience was the same as PB's.

[Demsy]

I too had to adjust the voltage everytime I change the driver tube, the voltage difference on some tubes reached 15volts.

[Paul Birkeland]

I too had to adjust the voltage everytime I change the driver tube, the voltage difference on some tubes reached 15volts.

15V on a 150V adjustment is within 10%, and not worth worrying about with the 300B Paramount.

[Demsy]

Haha, true, but I'd like to have the numbers close to the recommendation.

[Grainger49]

Pragmatically you can check the voltage after changing tubes and adjust if necessary.  PJ walked Paully and I through a way to put the voltage on the top plate of the Paramounts.  This requires a couple of resistors and a couple of diodes.

At the same time we went to Bourns 10 turn pots that came through the top plate.  So all adjusting was done without inverting the amps.

There is a thread about 2 years back in the Paramount folder.

[johnsonad]

I have an easier way then the one Grainger posted a while back as long as you are using 300B's. Keep an eye out for a thread on my latest amps (writing it now) and it will be detailed there.