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In Reply to: RE: your thought on this please . single GZ34 vs 2 x EZ81 parralell for preamp duty posted by lovetube on July 21, 2014 at 00:33:35
If it is low enough, don't count out 6X5GT (including the Bendix Red Bank version 5852) Or the 5Y3 and the 6106 Bendix version.
I generally pick a rectifier that matches about 50% to 75% of the load rating. Pulling 25mA from a 5AR4 that can handle 250mA is not a condition I would select.
Follow Ups:
hi C.
it draw around 25ma .
LT
25mA seems awfully low. Even for a simple gain stage unit.
Edits: 07/21/14
Hi!
Why double rectifiers for a mere 25mA?
Any of these will work nicely:
6X4, 6X5, 6AX5, 6BY5.
Or a pair of 6AX4, 6DE4, 6DQ4 if you want to be fancy
A single EZ81 should do nicely too.
Best regards
Thomas
Thanks Thomas.
the reason I thinking of using two rectifiers in paralell is to lower they impedance therefore lower impedance of the PSU
LT
Hi!
How much the impedance matters also heavily depends on the actual preamp circuit itself and also on the PSU scheme: full wave CT, full wave bridge, choke input cap input, etc. In my experience you won't gain a lot by doubling the rectifiers if anything at all. Over the years I went the other way and I got tremendously good sound results with high impedance power supplies others would laugh at.
Some of the TV dampers listed have very low impedances. There or others even lower, for example 6CG3, 6CJ3 are approaching the numbers of MV tubes.
If the impedance of the rectifier worries you, use solid state diodes,or a regulated PSU
Best regards
Thomas
"Over the years I went the other way and I got tremendously good sound results with high impedance power supplies others would laugh at."
Maybe some others, but by no means all would laugh; not everyone on these forums is of the "Low PSU Impedance" persuasion. These things need to be seen in perspective. A low current preamp, whatever Mu its tube(s) may have, is not going to give one iota of improved fidelity by feeding it from an "industrial strength" power supply.
I've even found slight improvement when going from an EZ81 to an EZ80 in one low-current preamp's PSU. It seems to be a matter of "horses for courses" IME.
The quality of tube itself compared to its peers more often makes way more difference IME.
In this instance, Mullard D Getter 50's EZ81 sound glorious (regardless of internal resistance) but Mullard may suck in another tube variety.
Naz
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