UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Reply
 
Thread Tools
Old 12th Aug 2020, 2:38 pm   #1
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Capacitor identification.

Hi, can anyone help me identify this capacitor please?
Given it's age, (1934) I'm guessing it's wise to replace it - but with what?

Many thanks

Ewan
Attached Thumbnails
Click image for larger version

Name:	IMG_20200812_143158.jpg
Views:	272
Size:	52.1 KB
ID:	213321  
Ewan Penkey is offline   Reply With Quote
Old 12th Aug 2020, 2:44 pm   #2
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,861
Default Re: Capacitor identification.

10uF 35V peak working electrolytic? The capacitance units appear to be obscured by the black wire.

What's the equipment?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 12th Aug 2020, 3:07 pm   #3
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Thanks for reply.

There's just a dash behind the wire - no units.
It's a Rickenbacker steel guitar amplifier.

So I guess I just need a small electrolytic.

Kind regards

Ewan
Ewan Penkey is offline   Reply With Quote
Old 12th Aug 2020, 5:38 pm   #4
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,861
Default Re: Capacitor identification.

Do you have a circuit diagram (schematic) for the amplifier?

Where electrically is the capacitor located in the circuit?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 12th Aug 2020, 10:35 pm   #5
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

No circuit diagram that helps with this component unfortunately.
The capacitor goes between one of the pins of the pre-amp triode and chassis ground.
The markings on the valve have been erased, but it looks very similar in appearance to a 76.
Ewan Penkey is offline   Reply With Quote
Old 13th Aug 2020, 1:52 am   #6
frankmcvey
Heptode
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 626
Default Re: Capacitor identification.

With that kind of working voltage, it's possibly a cathode bypass capacitor. The cathode would be Pin 4 on a 76's UX5 base. The valve base has 5 pins; 4 of them are equally spaced and one stands on its own. Looking from the bottom of the valve (or valve base) orient it so that the single pin is in the 12 o'clock position - Pin 4 will be the pin now at the 3 o'clock position, 90 degrees away from the singleton clockwise.

Is there also a resistor connected between the same pin and ground?
frankmcvey is offline   Reply With Quote
Old 13th Aug 2020, 8:46 am   #7
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 7,492
Default Re: Capacitor identification.

One thing,it will be very easy to re stuff and keep appearances correct for the year.
__________________
G8JET BVWS Member and V.M.A.R.S
HamishBoxer is online now   Reply With Quote
Old 13th Aug 2020, 12:24 pm   #8
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Thanks for your replies.

I've taken the photo oriented as suggested with the pin on it's own in the 12 o'clock position. The red wire is coming from the capacitor, and yes, that red resistor is in parallel with it. What type of capacitor should I use to replace it / stuff the original box with?

I think the resistor should be 2K6 but measures 3k7. Does that matter? All the resistors seem to be in the right sort of range, but still quite wide of the mark from what the colours would suggest. Is this something I should be concerned about?
Attached Thumbnails
Click image for larger version

Name:	IMG_20200813_121043.jpg
Views:	136
Size:	80.0 KB
ID:	213371  
Ewan Penkey is offline   Reply With Quote
Old 13th Aug 2020, 1:59 pm   #9
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,861
Default Re: Capacitor identification.

The red resistor carries a body, tip, spot colour code of red/green/red?? so should be 2.5k.

Replace the capacitor with an electrolytic type having a value of 10uF and a voltage rating in excess of 35 Volts.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 13th Aug 2020, 2:02 pm   #10
frankmcvey
Heptode
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 626
Default Re: Capacitor identification.

Yup, that's the cathode bypass cap. Given an unlimited sale price point, an amp designer would design an amplifier using components that would give the ultimate performance, so you could easily assume that everything in the amp was spot on spec, so you would just replace like for like. However, the amp designer would usually be given a maximum budget by the sales/accounts people so he would have to cut corners.

The cathode bypass cap, assuming that it is indeed 10uF, seems low to me, probably because this is one of the corners that he's cut - high value electrolytic caps would have been very expensive and bulky back in 1934 and you could replace it with a modern cap of a higher value, perhaps 100uF without incurring too much cost and incidentally improving the bass response of the preamp. A modern 100uF 63V electrolytic from Cricklewood electronics would cost 90p (incl VAT!) and easily fit in the old cap box. Watch out for the correct polarity when fitting it.

Those comments don't really apply to standard resistors, though - their prices would all have been pretty similar despite their resistance value, so we have to assume that the designer selected the best value resistors for the job. Manufacturing techniques were a bit more hit-and-miss back then, so their tolerances were fairly wide - typically 20% for standard resistors. So check your resistors and if they're within 20% of the marked value, they'll be fine.

If they're not within tolerance, you'd be best to replace them if you want the amp to perform to the design spec. What you'd use to replace them with, will depend largely on your aims. Virtually any modern resistor of the correct value and wattage will outperform those old dogbones in pretty much every respect.

What they will not do, however, is "look right" in a 1934 amp, so here you'll need to make a judgement call, whether you want your restoration to be period correct, simply functional, or somewhere between.

From your photo you'll also have to address the wax capacitors - these will very likely have gone leaky and will need replacing to avoid some potentially serious consequences.

HTH

Cheers,

Frank
frankmcvey is offline   Reply With Quote
Old 13th Aug 2020, 6:36 pm   #11
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Many thanks for all that helpful info. I'll go through the resistors again and check the tolerance is within 20%.
I may have to come back and ask how to calculate the wattage required and where to source resistors with a retro look at least.
I've already ordered some caps to replace the wax ones. Function has to take precedence over form on this occasion, as the owner (a band-mate) intends to use it on occasion with the "frying pan" steel guitar it was originally sold with. I'll give him a bag of the old duff components, so he can display them, or turn them into jewelry or something.

Thanks again.
Ewan Penkey is offline   Reply With Quote
Old 14th Aug 2020, 12:26 am   #12
frankmcvey
Heptode
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 626
Default Re: Capacitor identification.

Wattage info for dogbones attached - apparently info is from a 1936 publication.

I don't think I'd faff around, though - just use modern 2Ws all round. They won't look particularly retro, but the 2W size looks better than the tiny modern 1/2 and 1W resistors. Look on Farnell UK's website.

If you want/need to go down the retro route, you'll find info on YouTube for faking dogbones by moulding resin putty around modern resistors and painting the result.

Similarly, the paper/wax caps are usually quite easy to gut and restuff with smaller modern caps.

Replace your components one at a time and take plenty of photos before and during your working - you'll be surprised how often you have to refer to them. DAMHIKT!

Let us know how it goes.

Cheers,

Frank
Attached Thumbnails
Click image for larger version

Name:	Dogbone Resistor - size - watts (1).jpg
Views:	78
Size:	101.4 KB
ID:	213424  

Last edited by frankmcvey; 14th Aug 2020 at 12:34 am.
frankmcvey is offline   Reply With Quote
Old 14th Aug 2020, 10:08 pm   #13
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Thanks so much everyone.
Ewan Penkey is offline   Reply With Quote
Old 16th Aug 2020, 3:59 pm   #14
ColinTheAmpMan1
Octode
 
ColinTheAmpMan1's Avatar
 
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,322
Default Re: Capacitor identification.

You have a pretty old amplifier there. None of my Rickenbacker circuit diagrams show anything with a UX5 base, only B7G or B9G. There are only three Rickenbacker amp circuit diagrams, anyway and they are in Aspen Pittman's "The Tube Amp Book". I wouldn't mind betting that just about every component will be out of spec., it is so old.

To calculate wattage required of resistors, use Ohm's Law. It is W=IV and V=IR, so you can combine to get W=Vsquared/R, but it is good to add at least 50% more, or maybe even go for twice the calculated wattage.

Do you actually mean that the band-mate owns and is going to gig with an original Ricky "Frying-Pan" guitar? If it is what I think it is, he should take extreme care that it doesn't get stolen. I might re-think the whole enterprise, as these are truly old, rare instruments and although I hate to suggest it, they are almost museum-exhibits. I was going to ask if you can post some photos of the amp and guitar, but even that might be risky as this Forum is open to anyone to view.

Good Luck, Colin.
ColinTheAmpMan1 is offline   Reply With Quote
Old 17th Aug 2020, 8:07 am   #15
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Ok, I got the replacement cap and have scooped out the old guts and replaced with the electrolytic and fresh wax from my brother's bees. I'm really pleased with the result and it's inspired me to do a more authentic job with the other caps and resistors as per the YouTube videos. All the parts are ordered including the Humbrol enamels!

This amp (and it's frypan guitar) will only be brought out for special shows. Having said that, his "normal" gigging pedal steel is probably just as rare and many times more valuable than this amplifier. He believes musical instruments / equipment should be heard in the environment it was designed for, which I can empathise with.
Attached Thumbnails
Click image for larger version

Name:	IMG_20200816_195343.jpg
Views:	58
Size:	119.3 KB
ID:	213707   Click image for larger version

Name:	IMG_20200408_093432_9.jpg
Views:	53
Size:	116.3 KB
ID:	213708  
Ewan Penkey is offline   Reply With Quote
Old 17th Aug 2020, 9:33 am   #16
frankmcvey
Heptode
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 626
Default Re: Capacitor identification.

Glad to see that the first step has gone well. As Colin says, there isn't too much info on that amp around. There's a YouTube video of one being played here Your amp looks to be in much better condition, externally at least!

Another good YouTube source for vintage amp restoration is the "Uncle Doug" series of videos. He's very easy to listen to, explains things well and has a good balance of practicality coupled with respect for the age of the stuff he works on. He works on a Rickenbacker amp - one slightly younger than yours - here.

I know that your primary aim is functional restoration, but, that being said, it's a good thing to try leave the amp in a condition where a future restorer would be able to put it back into original condition if needed; in other words, don't do anything to it that can't be undone. Document your work and keep the old bits with the amp.

Good luck with the rest of it!
frankmcvey is offline   Reply With Quote
Old 17th Aug 2020, 12:27 pm   #17
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Noted - thanks!
I'm not sure anyone will want the black sticky mess I pulled out of the old capacitor box though - yuk!

I'm enjoying those links - Doug sounds great.
I've ordered that Aspen Pitman's book too - it seems like that's the bible.

Thanks again - I'll let you know how I get on.
Ewan Penkey is offline   Reply With Quote
Old 17th Aug 2020, 2:37 pm   #18
ColinTheAmpMan1
Octode
 
ColinTheAmpMan1's Avatar
 
Join Date: Jan 2012
Location: Wimbledon, London, UK.
Posts: 1,322
Default Re: Capacitor identification.

Quote:
Originally Posted by Ewan Penkey View Post
This amp (and it's frypan guitar) will only be brought out for special shows. Having said that, his "normal" gigging pedal steel is probably just as rare and many times more valuable than this amplifier. He believes musical instruments / equipment should be heard in the environment it was designed for, which I can empathise with.
I, too, empathise with the sentiment that musical instruments should be heard and not just displayed, but there are some dishonest blighters about who will nick anything that they know to be valuable. They have even stolen notable musicians' gear, when you would think that security should be like Fort Knox!

The Aspen Pittman book has now got to the "Deluxe Revised Edition", or maybe a step further. I have that and some of the earlier editions, too. It isn't cheap, is it? I do hope that the seller remembers to make a note on the Customs Declaration Form that it is "printed matter", otherwise you might get a nasty surprise from HMC&E. A reputable book-seller in the US ought to be aware of that and make the declaration. "Printed matter" doesn't get an import charge or VAT, you see.

Colin.
ColinTheAmpMan1 is offline   Reply With Quote
Old 17th Aug 2020, 3:10 pm   #19
Ewan Penkey
Triode
 
Join Date: Aug 2020
Location: Chertsey, Surrey, UK.
Posts: 20
Default Re: Capacitor identification.

Thanks Colin.
I managed to find it from a UK seller, fortunately.
Ewan Penkey is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:30 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.