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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 2nd Jun 2019, 9:35 am   #61
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Hi Frank yes that is exactly what I need. I will add a couple to my next order. Thanks.
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 5th Jun 2019, 12:15 pm   #62
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Quote:
Originally Posted by Nanozeugma View Post
In regard to rewiring, I don't think there is much of a convention regarding colours. The existing wiring will (as you have no doubt discovered) be either DCC (double cotton coloured) which, though eighty years old, will likely be perfectly serviceable and not need replacing,
This is very sound advice. I have traced all the circuit following the wiring diagram and apart from the mods that have been discussed and rectified every thing seems to be wired as it should. Both transformers are fine.
I am at the point now of purchasing replacement capacitors. There are four electrolytics, 3 8uf and 1 25uf all have which have been previously changed. Since these are connected across HT and ground I need to install components suitable for the voltages concerned. The rectifier valve UU4 states that the cathode voltage is 350 volts but one of the electrolytics (a can type non original) is rated at 500 volts. Am I OK to use capacitors rated at 450 volts for all four capacitors I intend to change?
There are obviously quite a number of paper capacitors to change but I feel it would be better to change the electrolytics first then bring the set up on a lamp limiter and variac as a test and if there is no magic smoke then set about the paper caps one at a time. Is this a good idea or is there a better way?
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 5th Jun 2019, 4:06 pm   #63
cathoderay57
Nonode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,364
Default Re: Unknown radio. Identified as a Murphy A34.

Hi Lynton, as well as the 2 transformers it is worth checking the continuity of the loudspeaker field winding which should measure between 800 Ohms and 2 kOhms. The speech coil is normally Ok and should be 1.5 - 3.0 Ohms.

You might not need to replace the electrolytics again if they have already been replaced. The 8uF high voltage ones need visually inspecting for signs of bulging of the rubber seal where the contacts are or any signs of gunge leaking out. If they are OK visually you might want to consider reforming them. Only attempt this if you are confident about working with exposed lethal voltages! For this you need a 200-300v DC power supply, a dc ammeter capable of reading at least 200mA dc and a 10kOhm 5 Watt resistor. For the power supply you could use the radio providing you leave the AC wires connected to the UU4 anodes and heater and disconnect the wire from the cathode to the 1st electrolytic HT capacitor. Solder on a new wire to the UU4 cathode pin and solder the other end to the 10kOhm resistor and connect the other end of the 10kOhm resistor to the positive lead of the ammeter. The negative lead of the ammeter goes to the capacitor positive terminal. The negative terminal of the capacitor or its can should already be connected to chassis but not necessarily. You need first to check that there is a low resistance between the negative connection of the capacitor back to chassis and/or the HT winding centre-tap of the mains transformer to complete the reforming circuit. Then switch on with the ammeter on the 200mA range. The capacitor should read a high current, probably 20mA or more to start with and then it should reduce slowly as the capacitor reforms. If after 20 minutes the current has not dropped below 1mA then the capacitor is scrap and you'll have to restuff it or just fit a new one. After you switch off beware because the capacitor will likely still be charged up to 400v and will give you a nasty shock. You can use the 10kOhm resistor across the capacitor terminal and can to discharge it safely then always measure the voltage to ensure it has discharged. Be careful if you are using a multimeter and remember to set the meter to the volts (not current) range when checking the capacitor voltage otherwise you might wreck your meter.

If you choose just to replace the 8uF capacitors then 450v rating is usually OK. For the first (reservoir capacitor connected to the UU4 cathode) choose a high-ripple type. For the low voltage 25uF capacitor (assuming it is a cathode decoupling capacitor on the AF output valve) they are cheap as chips so probably worth just replacing it. A voltage rating of between 25v and 63v is normally OK. You can test the 25uF capacitor if you have an analogue ohmmeter to see if it charges up OK (making sure you get the polarity of the probes right - sometimes on multimeters on the resistance range the negative probe carries the positive voltage).

You can use the multimeter to test the paper capacitors in the same way as well (on these test polarity doesn't matter) and if they show a low resistance then just replace them. If they show a resistance >5MOhms they will be OK to test the radio then you can measure any in-circuit leakage voltage while the radio is working.

Personally I don't use a variac but feel free to do so if you want. You should definitely reform or replace the high voltage caps before powering up the set as a whole.

Hope that helps. Cheers, Jerry.

P.S. I forgot to mention when you are reforming capacitors you cannot do it in-circuit i.e. you have to disconnect all of the wires from the capacitor first so that only the meter probe is connected to it

Last edited by cathoderay57; 5th Jun 2019 at 4:15 pm.
cathoderay57 is offline  
Old 5th Jun 2019, 8:30 pm   #64
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Hi Jerry thank you for the detailed and informative reply but maybe a little to hair raising (literally) for me! To be fair all the electrolytics are in poor shape. They are all from different manufacturers and one in particular is just dangling by its rubber coated wires under the chassis. I intend to leave the original cans in place for aesthetic effect but fit new components under the chassis. This will give me a chance to tidy up a common HT point which was only insulated using the old fashioned cloth tape. I have obtained new grommets and re mounted the tuning capacitor which was rather lopsided, and ordered some capacitors to move the project forward.
Lynton
Attached Thumbnails
Click image for larger version

Name:	C3DA16E8-5F82-4A67-B293-02DF3582FBD8.jpg
Views:	91
Size:	105.2 KB
ID:	184502  
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 8th Jun 2019, 1:03 pm   #65
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

More cleaning of the chassis last night but suffered a minor setback. When refitting the dial scale pulley (shown dangling in photo) it shattered! Seems to be made from a very soft alloy not unlike pot metal. Trying to effect a repair with crossed fingers.
In the same area the dial legend plate is in very poor condition (second photo) and I have found a few sites on the internet that repair such things but they seem to be American so the chance of a Murphy scale would be slim. Are there any tricks that can be done on domestic printers that would help rectify the problem?
Attached Thumbnails
Click image for larger version

Name:	86693259-BA39-4BBF-A6AE-6198CF1445BA.jpg
Views:	117
Size:	107.5 KB
ID:	184680   Click image for larger version

Name:	E88D571C-66FC-4C60-B233-262831F3D1F8.jpg
Views:	103
Size:	59.8 KB
ID:	184681  
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 8th Jun 2019, 6:40 pm   #66
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
Default Re: Unknown radio. Identified as a Murphy A34.

The dreaded Murphy "monkey metal".
__________________
G8JET BVWS Archivist and Member V.M.A.R.S
HamishBoxer is offline  
Old 11th Jun 2019, 7:23 pm   #67
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Powered the radio up for the first time this afternoon via a variac and lamp limiter. Nothing went bang and no magic smoke. The radio actually worked picking up R4 but with very low volume. Tried the volume, tone and bandswitch without any drama but when I switched in the ‘silent tuning’ there was no audio at all. Switched it back off and the volume had decreased. Next tried it with the lamp limiter out of circuit and the radio is now silent. HT is around 220 volts but didn’t have time to test anything else.
I guess I will have to check some valve voltages tomorrow. All the valves are getting warm, but nothing else is obvious.
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 12th Jun 2019, 3:17 pm   #68
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Took some voltage readings today with and without the limiter.
Still no sound from the radio other than a few crackles as I touched various pins with the test lead.
Looks like the rectifier and V1 are low on voltage, but I know V1 is in good shape so must be something in the circuit that is pulling the voltage down.
If anyone else has access to the circuit diagram I would appreciate some help.
Thanks
Lynton
Attached Thumbnails
Click image for larger version

Name:	9057857A-F7D9-47C2-9A17-8E9A3D392673.jpg
Views:	64
Size:	95.7 KB
ID:	184943  
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 12th Jun 2019, 4:12 pm   #69
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Unknown radio. Identified as a Murphy A34.

Is the mixer anode voltage in your voltage table 65 or 6.5 volts, difficult for me to tell.

Lawrence.
ms660 is offline  
Old 12th Jun 2019, 4:46 pm   #70
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Hi Lawrence It is 65 volts.
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 12th Jun 2019, 4:50 pm   #71
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Unknown radio. Identified as a Murphy A34.

I would check again, your voltage table shows that the anode of the mixer at 65 volts and the screen of the mixer at 11 volts, but according to the schematic the anode and screen voltages are in effect derived from the same point (the bottom end of R6) Also the osc anode voltage (11 volts) is the same as the screen voltage of the mixer, which seems a bit strange.

Lawrence.
ms660 is offline  
Old 12th Jun 2019, 8:21 pm   #72
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Hi Lawrence checked again and you are correct (must have checked wrong pins). Now with no limiter in circuit I get
Pentode anode 42 volts
Screen 42 volts
Cathode 11 volts
Triode anode 56 volts
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 12th Jun 2019, 8:36 pm   #73
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Unknown radio. Identified as a Murphy A34.

It might be worth checking C14 (0.01uF) for leakage.

Lawrence.
ms660 is offline  
Old 12th Jun 2019, 9:08 pm   #74
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Thanks Lawrence. I have no way of testing capacitors so I will change C14 with a new one tomorrow.
Thanks for the help.
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 13th Jun 2019, 2:48 pm   #75
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Lawrence you are a genius!! Changed the capacitor in question and the radio burst into life. Good reception on LW and MW and loads of volume. Unfortunately after a few minutes it went silent again. The rectifier was a little loose in the valve base! I have the chassis mounted on a frame so I can turn it any which way and the it had obviously worked a little loose. Now I can continue to replace the old paper caps one at a time.
If you are ever up in this neck of the woods I owe you a pint!
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 13th Jun 2019, 3:16 pm   #76
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Unknown radio. Identified as a Murphy A34.

So far so good, what are the voltages on the AC/TP like now?

Lawrence.
ms660 is offline  
Old 13th Jun 2019, 3:45 pm   #77
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Hi Lawrence voltages as follows (no limiter)
Pentode anode 171V
Screen 172 V
Cathode 4.5 V
Triode anode 96 V
A tad high but maybe my variac voltmeter is a little off.
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 13th Jun 2019, 3:57 pm   #78
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Unknown radio. Identified as a Murphy A34.

They're looking much better now.

Lawrence.
ms660 is offline  
Old 19th Jun 2019, 9:49 pm   #79
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

All capacitors changed, resistors checked and none are miles out of spec. Spent some time on the cabinet and with T cut, elbow grease, and Wilco scratch repairer it doesn’t look half bad. Youngest son is trying to reproduce the dial scale which is scratched and today I went looking for some speaker cloth. Found a place local to me which has more fabric than I have ever seen. Several nice ones to choose from for the speaker and finished up buying enough to do several radios for £1.87p. I don’t think they trade on the internet but I have their card and e mail address so if anyone is interested please send me a PM for details. The boss made me a new bag for the speaker so things are really coming together.
Lynton
Attached Thumbnails
Click image for larger version

Name:	99B858D3-BD10-4343-9626-AB6AE9AD4FFC.jpg
Views:	74
Size:	75.1 KB
ID:	185390   Click image for larger version

Name:	04CC9AD1-1CBC-453E-ABB4-1463A9AA71E0.jpg
Views:	78
Size:	91.7 KB
ID:	185391  
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Old 21st Jun 2019, 11:48 am   #80
LyntonP
Hexode
 
LyntonP's Avatar
 
Join Date: Nov 2018
Location: Greater Manchester
Posts: 305
Default Re: Unknown radio. Identified as a Murphy A34.

Quote:
Originally Posted by cathoderay57 View Post
You are extremely unlikely to find a good working AC/ME magic eye and the one that is fitted will almost certainly have no glow at all.
This is very true Jerry. The AC/ME does not work at all and as you say finding a replacement is probably impossible. The Valve Museum does not list any alternatives but are there any that would function without too much modification to the set?
Also the AC2/Pen DD has been substituted with an alternative valve along with some minor rewiring. Is the original valve available? I have looked on the internet without much luck. I wonder if anyone on the forum has one for sale?
Lynton
__________________
Never buy a mermaid a pair of socks!
LyntonP is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:27 am.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.