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Re: HexFreds in Tube amp?

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I have it the other way around, replacing SS HEXFREDs with a 5AR4. I got about a 20V decrease in B+ because the voltage drop over a tube rectifier is greater than the SS diodes. However, I was able to compensate for the decrease in B+ by changing other circuit parameters. If you change to HEXFREDs, you'll probably get a 20V or so increase in B+, which may be too much for the components and could damage something, maybe.

Personally, I like the 5AR4s. The sound is somewhat smoother and the bass seems to be "rounder" to me. HEXFREDs seem to give a tighter more dynamic bass with more impact, but I think you loose a bit of the midrange liquidity of tubes. Compared to regular N4007s, the sound of HEXFREDs was much more dynamic and resolved. I've also tried UF4007s with filtering, which DocB kindly suggested (See the latest issue of VALVE). These are supposed to be more tubelike in their sonic characteristics due to the decreased switching noise. I did find the sound to be smoother than with HEXFREDs while retaining the resolution. In general, my opinion is that you'll get tighter bass, but loose some of the tubiness of the 5AR4s(GZ34s).

Another idea is to try other tube rectifiers such as the 6Y3, GZ37 or 5U4. This would involve no soldering. Most of these will probably give you less B+ depending on the conditions. I'd be very interested in what you find.

I think it depends on what kind of sound you want. If you are really curious, I'd go ahead and try changing to HEXFREDs, but be carefull you might blow something out. Ideally, I'd measure the B+ while bringing up the power with a variac (I'm saying this without actually having done so since I don't have a variac :-). Also, see the safety tips posted elsewhere here or in the tweaks section. There's a useful tip mentioning the use of a light bulb for limiting current. You also should see what the maximum ratings of the various components are. There should be some room to push the limits a bit.

Other things to tweak include the PS caps, coupling caps and resistors. These components should also result in large sonic differences.


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  • Re: HexFreds in Tube amp? - bp 22:05:49 07/01/99 (0)


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