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 Mullard MAS15-34
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 Return to top of page · Post #: 16 · Written at 5:10:10 PM on 8 August 2018.
Brad's avatar
 Administrator
 Location: Naremburn, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 7395

There could be two versions - I find a 5 valve set (including eye) a bit under engineered for a radio that big.

There'd be room to punch another hole in the chassis behind the large valve in the middle.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 17 · Written at 3:29:13 PM on 14 August 2018.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2174

Well I'm sitting in my workshop listening to this old girl. It's got heaps of volume and the best tone I have heard on one of these old sets. The tuning valve shows no life but I haven't recapped yet. I am hoping its not a big issue . I just may need another valve or just contacts cleaned.


 
 Return to top of page · Post #: 18 · Written at 3:54:55 PM on 14 August 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5389

The big speaker makes a difference & that probably has negative feedback. With tuning indicators there is often a resistor of a round 1M on its socket: Rarely is that resistor in spec. Be careful with the metal Chinaman's hat on the small RF valve. Those can have the Bakelite inside the cap damaged easily by excessive force.


 
 Return to top of page · Post #: 19 · Written at 5:14:47 PM on 14 August 2018.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2174

Thanks for the advice,that's the first thing I will check Marcc . There is no sign of life at all in the tuning eye. I'm hoping this set just needs a basic cleanup.


 
 Return to top of page · Post #: 20 · Written at 6:02:08 PM on 15 August 2018.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2174

This one is a Six Valver I found two of the little buggers hiding from me when I pulled it apart.
I didn't do too much to it today I just replaced 3x .05s and cleaned all the valve sockets and plugs. It sounds a little better. I did check a .6 Meg resistor and a 150 ohm and both of them were in tolerance ( they were in the magic eye tube circuit. ) still no life from it. I will take it to my old mates place tonight and test the valve.


 
 Return to top of page · Post #: 21 · Written at 8:59:22 PM on 15 August 2018.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2078

The green glowing stuff in the old-style magic eyes can wear out completely, so it appears to be not working. There's no way to fix except by replacement - if you can find one.


 
 Return to top of page · Post #: 22 · Written at 9:30:24 PM on 16 August 2018.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2174

Robbert they are available but fairly expensive. Its worth the money to have it at 100% though. Its a EM1. At first we thought it was a EM4 but on closer inspection no.

I will have this baby completed very soon . All it needs is recapping and a tidy up plus some new speaker cloth and it will be pride of place.


 
 Return to top of page · Post #: 23 · Written at 11:55:45 AM on 17 August 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 1313

There is a slight possibility the cathode has run out of steam.
I recall seeing some suggestions of increasing the filament voltage and seeing what happens.
The lurk was to full wave rectify the feed to the tube and filtering that up to the peak value and trimming with a resistor.
A bit like boosting the heater on a CRT to flog a bit more life out of it.
Could be worth a try to prove whether its the plate or the cathode tired out?
Cant hurt a dud valve.
Fred.


 
 Return to top of page · Post #: 24 · Written at 12:00:49 PM on 17 August 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2476

You could use a 6U5 but it appears it's the green screen material that wears out, probably due to ion bombardment.

Have a look at this idea.

http://electronbunker.ca/eb/6U5.html


 
 Return to top of page · Post #: 25 · Written at 2:51:38 PM on 17 August 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5389

Careful that we are not putting the cart before the horse here. I prefer to go through the set, perhaps test the valves, but when I consider it a viable repair, I will get rid of the dodgy wire, caps & resistors before fault finding: Often they are the fault.

Leaking paper caps (most do, and badly) can drag down the AGC volts & that will seriously impinge on a tuning indicator (As well a the AGC & valve bias).

Sort that out, then panic, if the problem persists.


 
 Return to top of page · Post #: 26 · Written at 3:20:59 PM on 17 August 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2476

If the EM1 has heater and target volts it should light up irregardless of AGC.

Check for HT voltage on pin 7 of the EM1. If you get 200 volts or more here, the heater is lit but there is no green light, the EM1 is worn out.

Those magic eye green screens were generally only good for a few thousand hours.


 
 Return to top of page · Post #: 27 · Written at 4:31:16 PM on 17 August 2018.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2174

The Heater does light up. But nothing else.


 
 Return to top of page · Post #: 28 · Written at 8:45:19 PM on 17 August 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5389

Consensus: Speculation may be correct, but there is still the 1Meg resistor usually on the socket that has an attrition rate, plus what voltages, if any is on the pins?

Heaters light is a wonderful Flea Bay type statement.


 
 Return to top of page · Post #: 29 · Written at 10:21:40 PM on 17 August 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6761

Heaters light is a wonderful Flea Bay type statement.

That and "dial lights up and there was some humming -- probably needs a longer aerial".


 
 Return to top of page · Post #: 30 · Written at 9:06:01 AM on 18 August 2018.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2174

I should say I have had this valve tested by a professional tech. Yes the filament does light up but it's emissions are very low.


 
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