Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on April 21, 2015, 09:19:17 pm
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I have a PT that uses one of these with a pair of 6V6s in parallel and a pair of 12ax7s
I'm planning on swapping it all over to a more convenient chassis and building a 5F11 vibrolux
I've read that the 6X5 is less than ideal and didn't provide a lot of current
I could use solid state rectification but for this build I'd rather stick with a tube rectifier if i can
Any info on/experience with the 6X5?
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At only 70mA it looks to be inadequate for a pair of 6V6's, Also it wants to see a 4uF cap.
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Some of the '40s low priced amps had PTs with 70 MA for two 6V6s anyway.... Maybe the 6X5 was cheaper than a 5Y3 back then also (?)
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An EZ81 (6V filament) would work OK with a pair of 6V6s. A pair of SS diodes and a 100Ω to 250Ω resistor would give you that tube feel. Weber sells a SS copper-cap rectifier with built-in resistor in a tube base module.
http://www.webervst.com/ccap.html (http://www.webervst.com/ccap.html)
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Hey I forgot about the 6CA4, that's a good idea and I have a few
Also Solid state with a dropping resistor would be a good idea too
THanks!
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The PT sounds like it had a 2A 6V heater rating? 6V4G would be the next increment up if you had one, and didn't want to go over 2A.
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Talking about 6x5
I don't know if this is a typo, but I read 40uF as first capacitor
(http://www.mif.pg.gda.pl/homepages/frank/short/001/6/6X5.gif)
and in other datasheet 4uF (???)
http://www.tubezone.net/pdf/6x5gt.pdf (http://www.tubezone.net/pdf/6x5gt.pdf)
http://www.mif.pg.gda.pl/homepages/frank/sheets/121/6/6X5.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/121/6/6X5.pdf)
As far as I can know, I can increase the tube voltage handle using a pair of SS diodes in series, but .... there is a trick also to increase the
max first capacitor value ?
I've some 6x5 (may be 6x5gt) and I would like to use it at the best
Franco
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Both tubezone & Frank's say 4uF.
I think the simplest trick for more filtering is to follow the 4uF cap with a small value dropping resistor, then a a larger cap to feed the power tubes. That way the 4uF cap becomes a "pre-filter" to the 1st stage, and keeps the 6X5 happy.
A diode or resistor might work right after the 6X5 , basically substituting for an inductive input, I guess.
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Thanks JJasilli
Franco
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The transformer primary and secondary winding resistances play a part too. Perhaps best to try using PSUD2 to better identify what the steady state peak plate current will be.
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To further confuse things
On this amp a 6V6 pushpull unit
The main filter caps are 10, 30, 40, (uf) with the 10uf being the first stop after the rectifier
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Manufacturers are known to cheat with cap values after rectifier tubes. Even so, 10uF is still small and risks shortening the life of the rectifier tube.
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FWIW, Webcor used 6X5's in lots of tape recorders with 6V6s and 6K6s, usually less than 300V B+. They always put 20mfd or 25mfd caps as the first reservoir cap.
As for your 5F11 build up. Check the B+. If you don't have 330-340VDC with your donor PT, the 6X5/PT is not a good candidate.
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Should I be measuring that right at the rectifier? (which isn't currently hooked up to a filter cap?)
Or should I hook up at cap to get a better idea?
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Should I be measuring that right at the rectifier? (which isn't currently hooked up to a filter cap?)
Or should I hook up at cap to get a better idea?
Always put a cap on it.
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Perhaps if you measure the HT winding voltage and the primary and secondary HT winding resistances, then that would be a start to working out what DC voltage you would get , and what filter capacitance can be used.
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> say 4uF.
That is an Application EXAMPLE, *not* a Maximum Rating.
There's fine print about other cap values, if you read all which was written on the sheet.