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jazzbo 24th September 2008 05:03 PM

Hashimoto A-105 - summary so far
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Here is the story so far. Tested are 45, 46, ECC99, 5687, 12BH7A, 6S4A, 6GK5, all normalized to 1kHz. I'll post later on operating points for each tube. Still to test are 6N1P and 6C45Pi. If you'd like to see anything else, let me know. Enjoy!

kmaier 24th September 2008 05:46 PM

Thanks JB.... enlightening.

Have you tried putting a passive load on the secondary yet? Possibly a range from 20K to 100K (in increments) to see how this affects the output?

Regards, KM

jazzbo 24th September 2008 08:03 PM

No, I haven't tried loading the secondary yet. I've pretty much decided on a 9 pin driver in a 2 stage amp, preferably a dual triode because I can use the other half as a shunt regulator (this was done on the 5687 and 12BH7A). I'll go back to the ECC99 and try different secondary loads as you suggest. I've read that loading the secondary results in higher transformer distortion. Anyone care to comment on this? Also, does anyone have any opinions/preferences among the ECC99, 5687, 6S4A and 12BH7A as drivers? I know JandG expressed a preference for the 12BH7A in his IT amp. Anyone else?

re 12BH7A: the one I tested is a GE made in Canada. I also tried japanese and korean tubes. Both exhibited lower bias for a given plate voltage and higher rp. Anyone tried the russian EHs, and if so, how do they compare? NOS 12BH7As are getting pricey...

kmaier 24th September 2008 09:31 PM

Hi JB,

Are you able to measure distortion via test equipment? I would suspect running zero load (sans the IT inductance) that the driver is not seeing a consistent load vs frequency. This is probably resulting in higher distortion as the driver is not always in the linear operating range.

From feedback from another user (I can't test mine yet... over 4000 miles distance from them) loading the secondary actually reduced distortion and response was better.

As for prices... yea, they keep going up. Mike at KCA has GE NOS for $30 and RCA NOS for $35... Surplus Sales has RCAs for $19. ESRC has RCAs for $16. You do have some choices... NOS RCAs would be my choice. I would also suggest trying a 6FQ7, these are essentially a 6SN7 in a smaller 9-pin.

Regards, KM

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