+1 on the Panasonic TS-HA (400V), TS-HB (450V), TS-UP (500V). These are all rated for transient voltage 50V higher than nominal IIRC. To be conservative, select voltage rating based on transformer secondary X 2(sqrt2) since on start up without a delay of some sort the cold tubes won't conduct and the B+ voltage can rise to 1.4 X transformer secondary voltage.
Cornell Dublier 500V caps work well also.....you want high voltage, low ESR caps. 500V caps can be hard to find.....
Cornell Dublier 500V caps work well also.....you want high voltage, low ESR caps. 500V caps can be hard to find.....
Famous: if this is for your 350-0-350 transformer from your PSUDII thread, 500V caps are the best choice, since 350 x sqrt(2)=495V. That's what the B+ voltage will rise to when the amp is first powered on with cold filaments.
Change the current taps in your PSUD model to 1ma or .1ma each to confirm.
The 450V TS-HB's are rated for 500V surge and will probably work fine, but a 500V cap allows some margin. Exploding caps are no fun, and clearly 400V caps won't cut it with a 350-0-350 transformer.
EDIT: My post directly above should be transformer secondary x sqrt(2)......not x 2 sqrt(2).......
Change the current taps in your PSUD model to 1ma or .1ma each to confirm.
The 450V TS-HB's are rated for 500V surge and will probably work fine, but a 500V cap allows some margin. Exploding caps are no fun, and clearly 400V caps won't cut it with a 350-0-350 transformer.
EDIT: My post directly above should be transformer secondary x sqrt(2)......not x 2 sqrt(2).......
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Excellent info guys thanks!
"500V caps can be hard to find..... " This is exactly why I posted to the forum, it seems like the caps rated for 500v (illinois, f&t etc...) that a lot of websites offer I can't find datasheets for. Not to mention that I have found other threads claiming that those caps are all garbage.
I plan on having a standby switch after the reservoir cap to help against a hard start up.
"500V caps can be hard to find..... " This is exactly why I posted to the forum, it seems like the caps rated for 500v (illinois, f&t etc...) that a lot of websites offer I can't find datasheets for. Not to mention that I have found other threads claiming that those caps are all garbage.
I plan on having a standby switch after the reservoir cap to help against a hard start up.
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I don't know about undocumented 500 VDC caps being **** but they do probably have short life rubber seals in them. The typical can cap had a life of about 7 years. I've done the 525 VDC can cap in my ST70 3 times since 1971. The MacIntosh salesman measured the amp at 7 W/ch in 1971 and told me to replace the can cap, the rectifier, and the output tubes. In 1971 I used a bundle of axial Sprague atomlytics, which needed replacing in 1981. The CDE cardboard can cap I got from Stereo cost cutters in 1981 had about 10 hours on it when It leaked this year with new output tubes. This time I used 450 vdc nichicon radials rated 2000 hours up. Been using about 20 hours a week, 4 month life test down so far. No turn on delay components, but real 5AR4 rectifier tube. Did put a 47 ohm salvage 5 watt? resistor between the rectifier & the choke to slow things down at startup. With wall voltage creeping up 10 vAC since 1961 I am not worried about having enough power.
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Hammond power transformers usually run high voltage-wise, so the advertised 330-0-330 will probably be more like 350-0-350.............
Have you checked out Edcor's transformers? Nice prices, large selection...they'll even do customs for a $40 upcharge. 4-6 week lead time though. The output voltages are pretty spot-on for Edcor.
EDCOR Electronics Corporation
A lot of the old Al caps were +80/-20% tolerance. The modern caps are mostly +/-20%, so they are likely to be closer to nominal than caps in the past. A 47uF cap that is spec'd at +/-20% would be statistically closer to 40uF than a +80/-20% one. But statistics don't apply to single unit.
I would however expect the difference between a 33uF and 47uF to make a measurable differenece in tube life, albeit small.
Flip a coin, smaller cap - slightly longer tube life, slightly more hum / larger cap - slightly shorter tube life, less hum.
I would personally stick the 47uF cap in and not worry about it.
I would however expect the difference between a 33uF and 47uF to make a measurable differenece in tube life, albeit small.
Flip a coin, smaller cap - slightly longer tube life, slightly more hum / larger cap - slightly shorter tube life, less hum.
I would personally stick the 47uF cap in and not worry about it.
You didn't state a price range. If you just want the best possible sound, my favorite (other than the Blackgate WKZ series which are no longer available) are Mundorf MTubecaps. I have only tried the 100uf, 500v model but it sounds excellent by any measure. In some ways, I prefer it to my BG dual 100uf, 500v caps.
I just looked at some Edcor transformers and liked:
EDCOR Electronics Corporation. XPWR047-120
I guess the reason I am using the 5U4GB instead of a GZ34 is because I have a whole box of Tung-sol, Sylvania, and RCA just sitting around. So if life is cut short it's not a big deal if their will be a sound improvement.
I like Mundorf Mtubecaps but can't seem to find the dealers in the US.
EDCOR Electronics Corporation. XPWR047-120
I guess the reason I am using the 5U4GB instead of a GZ34 is because I have a whole box of Tung-sol, Sylvania, and RCA just sitting around. So if life is cut short it's not a big deal if their will be a sound improvement.
I like Mundorf Mtubecaps but can't seem to find the dealers in the US.
I bought my MTubecaps from PCX in Canada. They ship to US addresses. Here's a link:
capacitor_film_mund_mtube.html
capacitor_film_mund_mtube.html
If you are only pulling 55ma or so out of a transformer rated for 120ma, your B+ will be higher than you want. More series resistance can knock it down at the expense of higher PS impedance. This may actually be a good thing for a guitar amp if you want B+ sag for distortion purposes. Higher current rated PS transformers will have lower secondary resistance. You can play with that in PSUD. Unfortunately, if you call Edcor and ask them what the secondary R is for a transformer, they don't have that info. Ask me how I know that.....
Also, as you probably already figured out, the 5U4 drops more volts than a 5AR4/GZ34...not a problem, just something to keep in mind. Change your PSUD model to see. The 5U4 is a directly heated rectifier, so it warms up pretty quick, in a few seconds. The 5AR4/GZ34 is indirectly heated, and has a much slower warm up, like 10-15 seconds or so. That means you'll get more B+ overshoot with the 5U4 since it will warm up faster than the output tubes. Shouldn't be a problem if you use 500V (or possibly 450V TS-HB's) and/or you use a separate standby switch. I would build the amp to be idiot-proof, that is, if you switch everything on cold, you won't pop the PS caps, even though using standby will be easier on the caps as far as B+ overshoot goes.
How about two 68uf / 300V capacitors in series with 100K voltage balance resistors paralleling each capacitor? That's what I did for the reservoir for a project that used a 5U4GB with a 650Vct secondary to produce 350Vdc.
The ripple filter was a 7H Hammond ripple choke (open frame) with 220uF / 450Vdc behind for 58.64dbv of ripple attenuation. That made for a quiet DC rail.
What transformer make did you go with? I was warned that the Hammonds run higher than specified. Although I also heard that the 300 series by Hammond are more precise than the 200 series. I would like to obtain around 400 volts at the plate of my power tube (6L6GC).
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