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In Reply to: RE: "preventive not an "enhancement" " posted by 1973shovel on April 27, 2021 at 06:59:57
thanks for the reply confirming its a preventive measure...
my sarcasm was apparently missed re wire... but my point remains the same... whatever wire you use to filaments from the ps a 20awg lead on a uf4007 diode doesn't make sense... just don't use a sovtek gz34
Follow Ups:
...but perhaps your point about 20 ga wire on a 1 amp UF4007 does. I don't know what gauge wire the average transformer manufacturer uses to feed the plates of a 5AR4, but as long as it meets the current handling requirement necessary, where does your comment about it not making sense enter into it? The charts I just looked at indicate 20 ga wire is good for 1.5 amps, which is more than adequate.
As for your "don't use a Sovtek", I suppose that's one way to look at it. But from a belt and suspenders approach, as long as adding the diodes does no harm, then using them on a $100+ NOS Mullard is inconsequential, other than the bit of work to add them to the socket. Once the diodes are added, you have more tube choices, which to me is a good thing.
thanks for the follow up... you make a good case... appreciate it...
It's turned into an interesting exchange, so thanks for posing the question.
The big weakness in the Dyna ST-70 is the rectifier not the power tubes. If the amp is run at high power on an on-going basis, the rectifier simply isn't rated to handle it.
If you replace the rectifier, the voltages aren't good- you really do need its voltage drop to be there.
They really should have used dual rectifiers but price and size were constraints. So you have the case where even the best rectifier you can find will be the first tube to fail in this circuit.
The rectifier diode setup is nice for that reason.
Alternatively Triode Electronics of Chicago makes a drop in replacement power transformer that allows for dual rectifiers. You have to find an alternative filter capacitor arrangement but these days that's not hard. So you can used the filter can location for the second rectifier in parallel with the first. In this case the rectifiers will hold up much better.
The funny thing about this to me is it would have been cheaper and as effective to make a drop in power transformer that simply was designed for solid state rectification and got you the right voltages when so used. But I think they may have been concerned about loosing the controlled warmup of the 5AR4.
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