Hi Folks,
I’m trying to locate a replacement valve. Audio power tube 7 pin
15M-P19
Can anyone please assist?
It’s for a 1960s National stereo amplifier
Thx
Scott

Did not see in a hurry, but looks like its only designed for 100V & is a pentode often run triode wired

1. K & G3

2 &5 g1 (-6.7V 100V plate class A)

3&4 Heaters (did not spot volts)

6. screen (g2)

7. Plate.

It’s for a 1960s National stereo amplifier

National (Matsushita) tended to use some weird valves and configurations back then.

Radiomuseum list it with pin connections and voltages as Marcc indicated. It is an odd-ball with 15V, 0.3A heater.

Harold

I wonder if we can modify it to use something else of similar size.
Any ideas?

12AQ5 (12v 225mA heater version of 6AQ5) could be adapted.

Cheap, too:

https://tubedepot.com/products?utf8=%E2%9C%93&keywords=12aq5

You'll need to change a few pin connections and, if it's series heater and there are other valves in the string with 300mA heaters, shunt the heater with a 160 ohm resistor (two 330 ohms 1 watt in parallel is close enough) to match the heater draw of the original. Bias might be a bit different but since you are running on a low B+ voltage (are you?) it shouldn't be too critical.

If the heaters are being driven from a 15v winding on a transformer, you will need 13.3 ohms in series wit each heater. If there are going to be 4 12AQ5s from the same winding you'll need a 3.3 ohm 3 watt resistor in series with the winding. You get the idea I'm sure.

Is it one of a push-pull pair? If so, change both and bias them just like you would a pair of 6V6s.

Thanks Ian,
I'll probably only swap out the one defective 15M-P19 valve - was thinking a 6AQ5 actually as they specs are similar - its just the heater voltage that different - the other 3 15M-P19 tubes are fine and I guess rather than modify all things, just do whats required to get the unit working.
Cheers
Scott

It would pay to get the data sheet for 6AQ5 it's normally run at around 250V and the bias requirements will be different at 100V.

Marc

Here you go: https://frank.pocnet.net/sheets/093/6/6AQ5.pdf

And here:

https://frank.pocnet.net/sheets/079/1/12AQ5.pdf

How are the heaters connected? You don't want to use a 6AQ5 instead of a 12AQ5 unless the amp already has a 6 volt winding on the transformer.

Just changing one bottle may not be ideal if they both share the same cathode bias resistor. It will probably still work though and if there is enough negative feedback around it the distortion may be low enough that you could actually listen to it....

I'd change the pair. The data sheet above has data for class AB1 so you could work out the correct cathode resistor. Unless the circuit uses back biassing, then you might be in trouble. If this is the case you could lift the cathodes from ground and add some more ohms to augment the back bias.

It depends on what your B+ voltage actually is. It may well be more than 100 volts (which would be good).

"I’m trying to locate a replacement valve. Audio power tube 7 pin
15M-P19"

Sears PartsDirect (the spare parts side of the US department store) seems to have them in stock: https://www.searspartsdirect.com/part-number/15MP19/0057/528.html

I've bought some otherwise-unobtainable parts there before without issues. They won't ship outside the US, so you'll need a friend or re-shipper service to send them on to you. Also, I'd grab them soon - Sears recently filed for Chapter 11 bankruptcy, so there's a reasonable chance they might shut down their spare parts or fold altogether.

The 15M-P19 is a 15 volt version of the 30 volt 30A5 or HL94.

Apart from the heater voltage they are electrically identical.