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Please help Identify

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kolbep
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Username: kolbep

Post Number: 66
Registered: 05-2009


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Posted on Saturday, 13 March, 2010 - 01:48 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi All,
I decided to try my hand at restoring an 'antique' electronic item

Down in Margate, South Africa, these seem to be very hard to track down.

I just picked up this valve set at a 2nd hand dealer, and wondered if anybody had more info on it for me, before I even try to plug it in (series lightbulb of course),

here is the URL to the pictures
http://kolbep.webng.com/kolbep/album/Valve%20Radio/?id=25732

Thanks
Peter
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kolbep
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Post Number: 67
Registered: 05-2009


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Posted on Saturday, 13 March, 2010 - 02:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ok

bit of googling and it is a PYC 39G

Anybody know if I can get a schematic?

P
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kolbep
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Post Number: 68
Registered: 05-2009


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Posted on Saturday, 13 March, 2010 - 11:06 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Just to let all know, I asked the same details on the sci.electronics.repair newsgroup, and they are being extremely helpful so far.

The set actually works, with a bit of buzzing and other noises, but I will recap it to sort those out.

I have bypassed the o/c power switch, and can receive signals on most of the bands. So far I have identified a station from Johannesburg +-700km away, and that was using a 5ft cable for the antenna.

I can't wait till i recap this thing, then I will hang a long antenna and see what it really can do

I am pleasently surprised that this 1948 set is still working in a semi-respectable condition, and that i did not waste my money.

The only drawback is that it was only the chassis, and not the full cabinet, but still a good way to start on the tube path.

Peter}
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alan_stepney
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Username: alan_stepney

Post Number: 72
Registered: 01-2008

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Posted on Sunday, 14 March, 2010 - 07:00 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

By the look of it, a fairly typical Pye product.

Older radios/electronics often stay working, mush longer than people expect them to.
(Those Octal valves seem to have a long life).
I recently found a 1937 Philips radio at an auction, and once I had replaced the missing valve, that burst into life.

Changing the paper caps is often worthwhile, especially the one feeding the grid of the output valve.
The main electrolytics are also ones that need checking.

Good luck with it, although you will probably find that this is just the first of a collection!

As for the schematic, I'll see if I have one, or where you can get it.
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alan_stepney
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Post Number: 73
Registered: 01-2008

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Posted on Sunday, 14 March, 2010 - 07:11 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Paul Stenning has the service sheet for a similar set (Pye 39J/H) listed on his website:
http://www.service-data.com/

I suspect that that set, and yours may just differ in minor ways, for example, an additional band, or diferent power supply, or even just made in a different factory.
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kolbep
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Username: kolbep

Post Number: 69
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Posted on Sunday, 14 March, 2010 - 06:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Alan for that info, will check out the service sheet.
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zeitghost
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Post Number: 1453
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Posted on Monday, 15 March, 2010 - 08:36 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Looks very similar to the 19D that's decaying in my shed.
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kolbep
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Post Number: 70
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Posted on Monday, 15 March, 2010 - 05:51 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Zeitghost
I downloaded the service manual for the 19D, it is very similar. (some value differences, etc)

I just spent the last 1.5 hours (with some new braided cord from a tackle shop) restringing the tuner and dial, looks like that is checked off the list.

I also replaced the cap feeding the output valve, it was supposed to be 5nF, but was reading 1.5nF (thanks alan), and the set sounds a bit better.
I do not seem to have the same values with high enough voltages to change the rest of the wax caps, or the rectifier cap (2 in one can) {Does anybody know what I can strip - besides another tube set which I do not have - to get the other caps I may need.

Also the Output and Rectifier valves are running very hot (I can barely touch the Output Valve), is this maybe because the smoothing cap is kaput? Or is this normal.

I am thoroughly enjoying learning about how things were done in the good old days.

Peter
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steerpike
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Username: steerpike

Post Number: 474
Registered: 05-2005


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Posted on Monday, 15 March, 2010 - 10:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

RS Components has a very wide selection of components, and they will mail to you.

http://za.rs-online.com/web/

Better to buy new, since if you strip capacitors etc. out of similarly aged radios, they will be just as prone to failure as the one you are replacing.

With can-type electrolytics, modern ones are much smaller, so you can leave the original in place - but disconnected - and hide the new one under the chassis.

New valves you can get from "Mister Valve" in Johannesburg, also by mail order.

(Message edited by steerpike on 15 March, 2010)
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ant
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Post Number: 600
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Posted on Saturday, 20 March, 2010 - 09:48 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello Peter,

Most output and rectifier valves can - will, usually - run too hot to touch.

Regards Ant
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kolbep
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Username: kolbep

Post Number: 72
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Posted on Sunday, 21 March, 2010 - 09:01 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Ant, That is comforting to know.
I would like to scope the HT after the smoothing caps to see if they are still good (just so I can carry on till payday when I can order replacement caps for the set), but my scope has 5V/div with 8 divisions, which works out to 40V max (I think).

I do not have a probe with a pad on it.
Do you know how I can scope this without popping the scope.

Thanks
Peter
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ant
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Post Number: 601
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Posted on Sunday, 21 March, 2010 - 10:40 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello Peter,

Opinions seem to differ about old electrolytics; some say if it ain't broke don't fix it and some believe that they are timebombs waiting to happen. I prefer the latter view myself but I don't pretend to be an expert.

A simple potential divider would enable you to 'scope the HT - a pukka probe differs only in being better calibrated and, mainly, in being compensated for high frequency losses which are irrelevant here.

Regards Ant
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alan_stepney
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Post Number: 74
Registered: 01-2008

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Posted on Sunday, 21 March, 2010 - 03:56 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

As Ant said, opinions differ.
I tend to leave well alone, but check (if they are getting warm, then change them) and see if they are still OK.

Surprisingly, many that are far older than the makers could have expected, continue to work.
(Some makes tend to fail more than others, but that is little help as all you are really interested in, is the specific one in the set you are working on.)


If you have, or can get, a replacement for the main smoothing cap, then it is probably worth changing, especially if the rectifier is an unusual one, or the set hard to dismantle, purely to save potential work and cost in the future.
Not that I do that, but it is still good advice. lol
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twintub
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Username: twintub

Post Number: 83
Registered: 02-2007

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Posted on Sunday, 21 March, 2010 - 10:06 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ant,
Surely a potential divider is not required? If the scope already has a 1Mohm input, all that is required is a 9Mohm resistor in series with the input?

Peter,
Are you sure your scope has a max of 5V/div? It seems rather low to me - usually 20V/div is the norm. Some scopes specify that no more than 5V be applied to the input when set to 50ohm input impedance - most scopes have switchable 1M/50ohm inputs, while some scopes (expensive high-end types) only have 50ohm inputs.

(Message edited by twintub on 21 March, 2010)
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ant
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Post Number: 603
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Posted on Sunday, 21 March, 2010 - 10:16 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello tt,

I've no idea what the 'scope input impedance is; given that it apparently won't accept much input either, perhaps it's home-brew or otherwise to be considered a one-off? Whatever, a potential divider will do no harm and may do some good!

Perhaps Peter would enlighten us...

Regards Ant
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kolbep
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Username: kolbep

Post Number: 73
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Posted on Monday, 22 March, 2010 - 07:39 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi
The Scope is a Beckman Industrial Circuitmate 9020 20Mhz Oscilloscope.

The marking at the Ch1 and Ch2 Inputs are 1MOhm 35Pf, 400v peak max.

The same scope is on ebay :
http://cgi.ebay.com/BECKMAN-INDUSTRIAL-CIRCUITMATE-9020-20MHz-OSCILLOSCOPE_W0QQitemZ390170430661QQcmdZViewItemQQimsxZ20100318?IMSfp=TL1003181910012r17466

If you click on the picture it will supersize it so you can see the markings.

P
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mee
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Username: mee

Post Number: 41
Registered: 05-2010

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Posted on Monday, 31 May, 2010 - 10:07 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi kolbep. I wrote the following a few days ago, but after typing it, I realised that I wasn't logged in as I'd reformatted my drive. I'm not very good with passwords and things so it's taken until now to regain access.

I've posted the message as it was. Most of it still applies, apart from the bit about the protective circuit. Your Beckman scope should be fine with the valve circuit's HT rail,
provided that the rail is rated at under 400V DC.
I've got a fairly modern fast oscilloscope
that's got an input limit of 20V. My old Leader scopes handle 600V P-P or 600V DC.
Incidentally, 1Mohm at 35pF used to be a standard oscilloscope input impedance. I used to have a dual-beam (not dual trace) 5MHz Cossor scope with a maximum sensitivity of 5mV per division! Wish I'd kept it.

"Interesting kolbep. I've only just found this arm of the chat site. Here goes...

First thing that hasn't been mentioned -- and it's too late now anyhow -- is that you should have eased in any old electrolytics in the set by applying a low voltage to its input for about half an hour.

Preferably, this initial voltage would be a steadily increasing voltage, but that's not always practicable. Inserting another piece of mains equipment in series with the radio's mains supply would have sufficed.

Not sure whether I should advise this, but surprisingly, with a piece of kit this old, a tap to the valves *can* improve performance, particularly with the RF valves. If you do enough research, you might well find a valve resuscitation circuit. I've definitely got one, but it's be a xxxxxx to find.

I assume that since you haven't mentioned it, the speaker has a permanent magnet. Some early radios like yours had an electromagnet and used a hum-bucking coil.

An aquaintance of mine as a child had a huge US-built radio with such a speaker. It had a motor driven station pre-selector and way more than the 7 or 8 valves that were typical of most sets.

It worked, but it hummed. So all he wanted to do with it was throw the valves because he liked the pop they made. Very sad. What a moron.

If you want to look at ripple on the supply without risking your scope, don't connect your scope yet. Rather, connect a suitably rated capacitor to the rail and connect a suitable rated resistor to ground to remove the DC component. Connect a Zener diode over the resistor that's within the rating of your scope's input then, if you want accurate readings, leave the Zener in place and remove the resistor. I'm assuming that you know all the necessary safety precautions so this is without prejudice!

To look at mains hum on a valve supply, you'll need a fairly large non-polarised capacitor. I'd suggest about 1uF. That sounds small, but when it's rated at 4 or 500V...

Drat, I've just noticed your last post. I'm pretty sure that 400V peak means that the scope can handle anything up to 400V peak-to-peak, peak or 400V DC which, as you probably know, is very much less than 400V RMS.

Measure the DC rail in the radio with a multimeter. I guess it'll be between 250 and 350V. If that's the case, I would also guess that the scope can handle the HT rail without modification.

Cheers, mee"

Just remembered that the vast majority of valve radios had five valves.

(Message edited by mee on 31 May, 2010)
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zeitghost
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Username: zeitghost

Post Number: 1488
Registered: 01-2006

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Posted on Tuesday, 01 June, 2010 - 08:35 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ah yes.

Scopes with 10V limits on the input voltage.

As in expensive HP things that I cordially detest.

Still haven't found a scope I like more than the Tek 465 (unless it's a 475 or 485).

I used a x100 probe to measure the hum on a Philips wireless set.

That probe is good (according to the spec) for 1200V.

In a fit of madness I bought a x1000 probe about 20 years ago.

That's good for 15kV.

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