[glass_painter]

Hello All,

If you look at the Cymbal amp design you will notice that it runs with four 6h30p tubes in the output 15 ma each section.
Do you have an idea why was it designed this way instead of "half the tubes double the current" setup?
These tubes can take it with no problem.
Any insight will be appreciated.

Thanks.

Glass_painter

[hagtech]

These tubes can take it with no problem

That's not what I found.  The original prototype ran the same configuration but at 20mA each.  It was just enough to cook the tubes too close to their specified 7W total plate dissipation rating.  What happened was that the bias became slightly thermally sensitive and caused operating point shifts.  I backed off a bit on the dissipation and bias became rock solid. 

Secondly, the output impedance (damping factor) is a direct result of paralleled plate impedances.  Using half the number of tubes will roughly double the output impedance, making for less control of the loudspeaker and lower output power.

jh

[glass_painter]

Hi,

Thanks for the fast reply.

I was wondering if you had a chance to run this amp with 6n6p's, what was the result?

If not, do you think this worth while effort?

Thanks,

Glass painter

[hagtech]

had a chance to run this amp with 6n6p

Well, today is the first I ever heard of this tube.  However, on quick inspection it looks like maybe you could make it work.  Not sure it can handle the power dissipation, nor is it capable of delivering high currents.  I didn't check pinout, but it will likely operate in a CYMBAL circuit, just not sure how well.

jh

[glass_painter]

Thanks Jim for all the information.

Glass_painter