Recapping old tube equipment...

[eccerr0r]

If there are any caps worse than these counterfeits, it's these tube equipment capacitors after many, many more years...

Unfortunately I don't have many spares, especially the dual section caps. I wonder if anyone had tried using the (modern) switching power supply caps, despite them holding much more energy, to replace older caps. Perhaps an additional resistor or NTC resistor is needed to stop inrush but any other issues? Killing rectifiers due to the inrush?

I have this old tube radio that uses a 90 and 80 uF dual section cap. Now I have a few 470uF caps from dead PSUs...

[rhomanski]

Re: Recapping old tube equipment...

Try these guys. https://www.tubesandmore.com/ . This one might work. https://www.tubesandmore.com/products/C-EC100X2-500 .

[goontron]

Re: Recapping old tube equipment...

Though these guys can be cranky old Bastards at times, its still the best forum for antique tube radios.

[jojo69]

Re: Recapping old tube equipment...

I believe the only source for the multi section cans is N0JMY over at hayseedhamfest.com

[goontron]

Re: Recapping old tube equipment...

Though these guys can be cranky old Bastards at times, its still the best forum for antique tube radios.

link needed, eh?
http://antiqueradios.com/forums/

[eccerr0r]

Re: Recapping old tube equipment...

I'm just cheap I guess. Basically need to hold out as long as I can until I perhaps pick up some better replacements when I can find them at a better price.

In this case I have a radio that someone had recapped a 2-section radial ~90uF/60uF with two very large axial 100uF caps. So basically they're hanging there with two of the leads twisted together before getting stuck in the board. I was thinking about drilling extra holes into the pcb and using more modern caps, hopefully more stable than what it is now...

[stj]

Re: Recapping old tube equipment...

better to use a pair of new caps, than some NOC (new old crap) that has been re-formed but probably has a hardened bung and crystalised electrolyte.

[eccerr0r]

Re: Recapping old tube equipment...

Fortunately the radio is one of the "cheap transformerless" non-doubled designs, so voltages shouldn't get near the 500V mark. A 160-200V should be sufficient, possibly closer to the 200V mark due to the silicon rectifier in this unit...

Sometimes I wonder if nothing but 105C capacitors should be used in tube equipment as they can generate as much heat as modern computers...

[stj]

Re: Recapping old tube equipment...

maybe you should even look at 125' parts if it's that bad.
mostly though, the valves are on top of the metal plate, the caps & resistors on the underside - except the big can caps.

[eccerr0r]

Re: Recapping old tube equipment...

Alas this is one of the "cheap transformerless" designs so there is a PCB, and most components are on the top side. I should take an IR thermometer and probe near the caps to see how hot it really gets after leaving the cover on, but the 50C5 tube definitely gets *quite* hot. Not sure if the IR thermometer is reading the glass temperature or the plate of the tube (likely the latter) but I seem to recall it was well over 300F...

[redwire]

Re: Recapping old tube equipment...

Don't be tempted to upsize the power supply filter caps by much. Bigger means higher peak currents for the rectifier. A 35W4 can feed 8-40uF.
Tube gear puts the can electrolytic right next to the rectifier tube which cooks the caps.
If a 50C5 is running too hot, the cathode bypass cap/resistor or coupling cap could be bad. It likes at least -7V bias on 150-180 ohms. But they can run 400F at max. ratings, good in winter....

[stj]

Re: Recapping old tube equipment...

maybe putting in a small fan away from the valves just to draw the hot air out?

[goontron]

Re: Recapping old tube equipment...

maybe putting in a small fan away from the valves just to draw the hot air out?

good luck deriving a stable 12v source.

[eccerr0r]

Re: Recapping old tube equipment...

Fan? in audio equipment? :o
I guess I do have some 120VAC muffin fans but maybe it's fine just to replace the caps once in a while, as long as they're cheap...

... as long as the tubes don't fry.

Anyway this radio doesn't have a 35W4, it uses a silicon rectifier for power. What really got me was that this thing actually has a varactor diode for AFC...

[stj]

Re: Recapping old tube equipment...

good luck deriving a stable 12v source.

where there is a will, there is a way.

last time i had a similar problem, putting 12v fans into some mains equipment - i used the pcb from a wall-wort psu.

[eccerr0r]

Re: Recapping old tube equipment...

First a fan, now switching PSU in audio equipment? Are you nuts?

I wonder how big of a cap would be a "direct replacement" of the old 90/60uF caps, 100uF is probably fine (and it is!) but I wonder if I can safely go to 200uF perhaps...

I also noted there's a wire link that shorts out where there used to be a resistor. I wonder if I should just swap that shorted link out for a NTC thermistor...

Perhaps this will get the (really) faint 60 cycle hum out to nothing. Then again it might just be the cathode heaters inducing that noise...

[juliadream]

Re: Recapping old tube equipment...

Don't be that worried about the heat rating.. they weren't fussed in the 60's and modern components are far superior to anything they used back when. Personally I would test what you have on full voltage and if it ain't broke don't fix it, unless it's obviously in distress.. bulging, leaking etc. I have a main smoothing block in a Vortexion 40/60 date coded 6/1944..(d day!) it's fine.. I just make sure to run it up every 6 months or so to keep the caps formed.

How about restuffing with say 100u @ whatever volts the originals say? .. take note of the "max ripple" otherwise with tube stuff.. "near enough" is fine as long as over rating ..

You wouldn't believe some of the "austerity" (1950's) era repairs of old gear I have seen in my time.. fuses replaced with nails, lost centre taps on power transformers made good by a pair of 100 ohm wirewounds across the filament (direct heated rectifier) winding to make a centre tap for ht+ !! single output pentodes replaced by 4 ancient UX4 rf triodes in parallel with the wires held on with twisted loops and wax and tied down to the chassis with string !! :O

Ideas from the other side of the pond on restuffing those bad boys.. http://www.vintage-radio.net/forum/s...d.php?t=107115

[SteveNielsen]

Re: Recapping old tube equipment...

Back in the heyday of tube gear there were small ac powered box fans some folks used for cooling.

[eccerr0r]

Re: Recapping old tube equipment...

I was just thinking about doing a "proper fix". The two (huge! Each probably physically about 75% of the original, together they are 50% larger than the original 2-section) axial caps, due to the extra lead wires, make the caps dangle in position. No shorting threats at least, but it just looks a bit tacky floating there and these "repair" caps themselves look a bit old now as well.

They do work however... Perhaps "if it ain't broke, don't fix it" is the proper course of action...

[mockingbird]

Re: Recapping old tube equipment...

Be careful with those axial caps that are very popular within the vintage radio/tv community...

They're almost always Taiwan source, and suffer from all the other inherent deficiencies of ordinary Chines caps.

You're always better off just purchasing radial Japanese caps, and modifying them on your own.