Plate voltages in Bluesmaster amp?

[Mark]

I have put all the power supply resistor string values (choke > 3.4K > 15K > 10K > 150K shunt resistor) into my 50 watt Bluesmaster clone (Boogie SOB is the donor amp).

I'm finding the voltage aren't the same as what others have noted.

I'm currently using GT12AX7M valves. The plate voltages are around 190VDC for V1, 220VDC for V2 and 270VDC for the PI valve.

It found installing the 150K resistor really loaded down the plate voltages on V1.

I will try and put other valves into the amp and note the voltages. Though I would think a 5VDC difference would be typical, not 30VDC.

Any thoughts?

[Mark]

As previously mentioned the voltages in the pre-amp are as follows;

V1a = 195VDC, V1b = 202VDC

V2a = 220VDC, V2b = 222VDC

V3a = 280VDC, V3b = 269VDC

I then tried shuffling them to the right; (V2 became V3, V3 became V1 etc);

V1a = 204VDC, V1b = 214VDC

V2a = 214VDC, V2b = 220VDC

V3a = 277VDC, V3b = 261VDC

I put some used O.S. Mullards into the pre-amp;

V1a = 188VDC, V1b = 196VDC

V2a = 210VDC, V2b = 215VDC

V3a = 272VDC, V3b = 270VDC

I didn't expect a 10VDC difference between valves, so I dare say I will wait till I get the new JJ 83's and JJ803. I'll measure again and post results.

I'll let them settle in and make adjustments to the power supply string.

[glasman]

What you are seeing is typical for various tubes and even within the same manufacturer.

+/- 5% plate voltage swing between tubes is pretty normal. The only way to get around this is to group tubes based on their measured characteristics. But this is a TOTAL PITA .

When I order tubes I spend a few hours measuring every tube and listing the values on the box. Based on the measured values I determine what slot I will use a particular tube.

[Mark]

Thanks for the reply Gary. That does make putting tubes in the amp a PITA. Typically, I'd only want to buy the tubes I need and not a cast of thousands.