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Old 2nd March 2012, 12:42 PM   #1681
kmtang is offline kmtang  Canada
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Dear Albert,

The next try is to experiment the effect with different HT filtering cap. You would be surprised for the difference it makes.

Brother Johnny
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Old 2nd March 2012, 01:05 PM   #1682
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Nothing surprises me with caps. I just spent a while auditioning bypass caps for a 46 driver stage for a 300b SET. In the end no cap was best - this preserved the harmonics and life in the instruments. A really good 47uF polypropylene (big ICW SA) was a bit flat sounding. A cooking ICW poly was a bit more flat sounding and an electrolytic sucked all the life out of the music - quite horrible. With the caps it all sounded very tidy - possibly even a bit less intermodulation distortion in the treble - but by God it was boring to listen to. What's the point of DHTs if you kill the sound with cathode bypass caps. A shame I can't use filament bias easily on a 46. Next best is battery grid bias or a really good unbypassed cathode resistor. Now, 0.1uF Russian teflon FT-3 I can live with easily, but that's about it for caps. In the PSU all polypropylenes.

andy
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Old 2nd March 2012, 01:20 PM   #1683
FRUGIVO is offline FRUGIVO  Spain
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hi all
andyjevans a question for you as an expert in this topic
what is your favorite tube 26 all versions available
according to your taste aurally speaking
thanks in advance

pedro

Last edited by FRUGIVO; 2nd March 2012 at 01:23 PM.
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Old 2nd March 2012, 01:24 PM   #1684
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Hello Pedro,

I'm not fussy about 26s. These are old tubes and condition will be more important than the make. I have a slight preference for globes so I prefer to use those, but the ST ones are nearly as good. I mostly just pull them out of my drawer and plug them in!!

andy
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Old 2nd March 2012, 01:41 PM   #1685
regal is offline regal  United States
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Quote:
Originally Posted by andyjevans View Post
What's the point of DHTs if you kill the sound with cathode bypass caps.

andy
This is where I am with DHT's (headamp/preamp), I find the biggest virtue to SET sound is with a good shunt reg big caps are kept out of the loop and the sound great. The nice thing about the 4P1L is higher gain and the filament bias without a cap along with good output impedance, a #26-pre with 4P1l-300B might be a good alternative to the #46 ?
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Old 2nd March 2012, 01:51 PM   #1686
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Quote:
Originally Posted by kmtang View Post
Dear Albert,

The next try is to experiment the effect with different HT filtering cap. You would be surprised for the difference it makes.

Brother Johnny
Brother,

Will try different caps when available.
Thanks for the stand-off strips. It works perfect.

Albert
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Old 2nd March 2012, 02:02 PM   #1687
работник
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Quote:
Originally Posted by andyjevans View Post
Nothing surprises me with caps.

<snip!>

A shame I can't use filament bias easily on a 46.

andy
Andy, you can do a variation on filament bias for DHT 46, if you are really interested to try it.

1. Heat the filament with a proper regulator in the usual way
2. Take a second filament regulator, configured for 330mA, connected to a 38V supply.
3. Use an unbypassed 100-ohm cathode resistor.
4. feed the 330mA into the resistor, as if it were the filament current. This generates your -33V bias. Using a high quality current-driven regulator avoids degrading the quality of the 46 stage.
the 100-ohm resistor dissipates 10W, as per the DHT-26 case.
5. The unbypassed Rk 100-ohm decreases the effective gm from 2.35mA/V to 1.9mA/V, - far better than the 0.52mA/V from using an unbypassed 1500-ohm resistor.
6. Enjoy cap-free sound.


.
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Old 2nd March 2012, 03:07 PM   #1688
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Sounds ingenious - have you tried it?

Andy
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Old 2nd March 2012, 04:08 PM   #1689
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I used it on an indirectly-heated pentode driver for 300B, again 300mA. It enabled a single-stage to go from line to 300B, without cathode caps. (Now, I use a shunt cascode with EF184s, again without bypass - the best 300B driver of all).
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Old 2nd March 2012, 05:08 PM   #1690
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Quote:
Originally Posted by Rod Coleman View Post
EF184s, again without bypass - the best 300B driver of all).
I don't know exactly why but this made me think of Spinal Tap - "It's in D minor - the saddest key of all".....

Maybe your CLASH logo......!

Andy
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