resistors and capacitors out of tube radios -acceptable quality for diy amp?

[Poppy]

Hi,


as probably all of you are aware of, prices for resistors and capacitors are not that super low anymore as soon as they are required to endure some higher voltages/powers like the ones occur in tube amps. Furthermore is it much less fun having to order and wait for each component than being able to experiment around straight away -which requires to widely assorted at home.


How about getting a few hopeless broken tube radios for components? Would you recommend to use them when money is a concern? Or do these prices for suitable and new resistors and capacitors have to be paid no matter what if demands regarding results are not given up?


Thank you!


Poppy

 

[Le Basseur]

Short answer:NO. (except,maybe,some military or industrial equipment components).

 

[JonSnell Electronic]

£74 for 100 of each value;
https://uk.farnell.com/multicomp/cf...170595&searchref=searchlookahead&exaMfpn=true


Last you a few years.

 

[Kay Pirinha]

I built amplifiers and many other things from parts that were butchered from old TV's and radios in my youth and as a young student simply 'cause this was the cheapest way to get parts at all. Some of these units still are in service until today, for instance my Elektor Crescendo that I built in 1885: Update for Elektor Crescendo Power Amplifier 1982
Best regards!

 

[OldHector]

Hi Kay, very nice! What was the tube amplifier lurking in the background?

I always think it is interesting that no one will fit secondhand tyres to their cars, but no one replaces the tyres when they buy a secondhand car.

The best pickings I have had for old parts so far was an old tube Tektronix 535 oscilloscope. I'll never be lacking a 6DJ8 or quality amphenol tube sockets.

Rgds,

Richard

 

[Kay Pirinha]

Hi Richard,
this tube amp I've built around an ECC83, an ECC82 and a pair of EL34's per channel. The ECC83 ist the PI right at the input, followed by a symmetrical voltage amplifier feat. the ECC82 and the EL34 pair in class AB. So this amp is fully symmetrical. I've wound the OT's by myself, but bought a custum wound 300 VA toroidal PT.
This amplifier is in it's present state since about 1995, but had developed from another one that I built to make use of a RIM Electronic Hercules PT that I've bought many years before for cheap. The original amplifer used the same chassis and comprised a ECC82 cascode at the input, followed by a DC coupled ECC82 PI and then the EL34 pair. I never was too happy with this amp due to it's rather harsh sound - despite it's flawless square root prformance even at 10 kHz. As I didn't manage to improve it (where should I have started if the 'scope showed no issues? Perhaps the cascode's gain was just too high?) I decided to redesign it as described at the beginning.
Should I show some pics of it to you?
Best regards!

 

[OldHector]

Hi Kay,
interesting that the sound was harsh without being able to measure the reason. Our ears have their own agenda. I was reading te Norman Karen website, and he had some information about the different ways that men and women perceive sound; from his site, women have to be able to detect the squall of a child, so are more sensitive to high frequencies, whereas men have to perceive the footsteps of a distant mammoth (!), so are more sensitive to low frequencies ;-)

Yes, the photos would be interesting, as long as the OP does not mind!

Rgds, Richard

 

[Fenris]

I would say no. I inherited a bunch of unused resistors and caps from my grandfather (he built electronic organs for churches). They were all of '70s / '80s vintage, so newer than most tube amps. I can't use them because their values are randomly all over the place, sometimes half the marked value. It may have to do with them being in a humid environment (Florida) for decades. Modern caps and resistors are much improved in quality and reliability over those made even 20 years ago. I don't trust old resistors at all, or old (25+ years) electrolytic caps. Sealed film capacitors are probably good for over a half century, but should still be tested. Very old transformers I worry about, especially those with cotton insulation on the wires since it tends to degrade.
Personally, the risks just aren't worth cutting corners. Of course, 15 years ago I bought about 50 pounds of assorted resistors on tape from the leftover reels of a factory. Enough varied values that it will probably last the rest of my life.

 

[painted]

Soit, it depends. I am stocking a life time quantity of unused telecom and computer electrolytic capacitors from the 70s and 80s. Ok, each cap needs to be formed before usage but that takes 15 minutes at most. It is high quality stuff coming from France if I remember right, double the size of modern equivalents (with a shorter lifespan at the same ripple current and used under same operating temperature).

 

[audiowize]

as probably all of you are aware of, prices for resistors and capacitors are not that super low anymore as soon as they are required to endure some higher voltages/powers like the ones occur in tube amps.

I completely disagree with this statement. Where are you located? What's "too expensive"? What's your time worth to pull these junky worn out parts out of old equipment?

 

[mondogenerator]

Soit, it depends. I am stocking a life time quantity of unused telecom and computer electrolytic capacitors from the 70s and 80s. Ok, each cap needs to be formed before usage but that takes 15 minutes at most. It is high quality stuff coming from France if I remember right, double the size of modern equivalents (with a shorter lifespan at the same ripple current and used under same operating temperature).

Anyone that says they can successfully reform a capacitor in a mere 15 minutes is lying, or fooling themselves.

 

[rayma]

Inexpensive resistor and capacitor assortments are available from many vendors, just look.
You won't have to wonder about, or test them. Still, avoid carbon composition types.

 

[rayma]

Anyone that says they can successfully reform a capacitor in a mere 15 minutes is lying, or fooling themselves.

Many electrolytics need an hour (or several hours) to reduce the leakage current to nominal levels.

 

[mondogenerator]

Totally agree.

The 3300uF 400V ones I recently reformed took several hours (isnt there a rule of thumb for hours per 1000uF?)

Either way, it took maybe 8 hours to get leakage below 50uA and within original as new specifications.

 

[mondogenerator]

(isnt there a rule of thumb for hours per 1000uF?)

Correction, its something like 1 hour reforming time, per year of correct storage (cool dry etc), and if that doesnt form them to original specifications then they're junk.

 

[Francois G]

.....Some of these units still are in service until today, for instance my Elektor Crescendo that I built in 1885: ....

Kay, I didn’t realize that you are that old, and well ahead of everyone one else in 1885

Kind regards!

 

[mike567]

I will some times use scrapped capacitors less than 5 years old) but resistors why bother?

 

[Eli Duttman]

IMO, old 'lytics should always be regarded as trash. Even if they, as is unlikely, have not dried out, reforming doesn't deal with a (quite unsatisfactory) high equivalent series resistance (ESR). Remember, the reservoir and decoupling caps. are in the signal path.

 

[Kay Pirinha]

Well, I've been frozen for several decades .
Best regards!

 

[painted]

Nonsense, they reform on the job in the next couple of weeks to minimal leakage current. These are unused elektrolytics, not worn out crap. I watch the current they take and slowly turn up the voltage, without a current limiting resistor and above the original working voltage limit. Trust me, I know what I am doing. Ever witnessed this process in a plant?