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I am building a SET amp using the VT-25 and I was wondering if VT-25A can be used interchangeably?
Thanks,
Min

Looks like the vt-25 and the vt-25a are identical, and both are identical to the 10.

http://www.nj7p.info/Common/Tube/SQL/Tu ... Type=VT-25

http://www.nj7p.info/Common/Tube/SQL/Tu ... ype=VT-25a

http://www.nj7p.info/Common/Tube/SQL/Tu ... hp?Type=10

Look at the high load resistance for Class A amps in the 10: 10.2-13K.

The Plates are larger on the 25A's , and the VT 25 filament is much brighter if I remember correctly .

What about the 801A. How does it compare to either the VT-25 or the VT-25A?

battradio wrote:The Plates are larger on the 25A's , and the VT 25 filament is much brighter if I remember correctly .

I meant that they are electrically identical: same max plate voltage, same max plate dissipation, same current draw on the filaments, same filament voltage, same transconductance, same mu, etc.

The 10, vt-25 and vt-25a are interchangeable. Don't expect more than 1.5W audio output for one tube.

http://www.nj7p.org/Common/Tube/SQL/Tub ... ?Type=801a

http://www.nj7p.org/Common/Tube/SQL/Tub ... ?Type=801a

It is a 20 watt tube as apposed to the 1.5 watts of the 10 and 600 volts B+ .

7W audio output in SE A2:



http://www.diy-audio-guide.com/801a-amplifier.html


8w audio output in SE A2:



17W audio output PSE:

http://www6.plala.or.jp/Michi/801A/Thre ... 7Wamp.html

Thanks all for the info and suggestions. I am actually building this one (ignore all the side notes made for the 45):

I have a couple of questions on this schematic:

1) I see that the heater voltage is 7.5 volts for the VT-25. Per the SUn Audio VT-25 schematic above, would the rectified 6.3 volts followed by 1000mfd/10vdc supply 7.5 volts for the heater?

2) Am I correct to assume that the primary impedance for the VT-25 is 10K?

Thanks,

Min

SDS-PAGE wrote:I have a couple of questions on this schematic:

1) I see that the heater voltage is 7.5 volts for the VT-25. Per the SUn Audio VT-25 schematic above, would the rectified 6.3 volts followed by 1000mfd/10vdc supply 7.5 volts for the heater?

6.3V through a FWB yields more than 7.5V. You may need to chop it with a resistor, but the loading and the hum pot could take 1.3V off.

6.3 / .71 = 8.87

2) Am I correct to assume that the primary impedance for the VT-25 is 10K?

The transformer has 8k and 5k primary taps. It looks to me like the 8k tap is being used. In the specs and other schematics, ~10k is the most common.

If you can only find a transformer with a 5k primary, putting 8ohm speakers on the 4ohm tap will get you 10k.

http://tubes.nekhbet.com/trans.shtml#spe

Perfect! Thank you. Min

kheper wrote:6.3V through a FWB yields more than 7.5V. You may need to chop it with a resistor, but the loading and the hum pot could take 1.3V off.

Use the Schottky bridge from the get*set*go, Min. It appears that I was getting a little over 7.1Vrms at cap #1. Depending on your filament transformer you might be able to squeeze in another RC. Definitely use 10000uF or higher.

Shannon