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 6AR7GT
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 Return to top of page · Post #: 1 · Written at 10:43:16 PM on 11 May 2017.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 339

Help please! Does anybody have one of these surplus to their requirements which I may buy, or know where I may obtain one?
I am desperately seeking one for my AWA Radiola 509GY. The 6AU6 was microphonic, which I have replaced, but the 6AR7 GT remains cold as Ice and gives off no light, so it seems that this is why my radio is not working, yet the phono works well. This is one valve which does not seem to show up wherever I search?


 
 Return to top of page · Post #: 2 · Written at 11:56:53 PM on 11 May 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2626

Some valve heaters are hard to see & that one has non standard pin outs for an octal: Only AWV data appears on Franks electron tube pages albeit it is listed in Philips data book. Check with an ohm meter between pins 1 & 8 for continuity.

Plate is pin 3: Screen, pin 4; D2, pin 5; D1, Pin 6; Cathode, pin 7; Shield, pin 2. Its a remote cut off Pentode Double Diode.

If there is a circuit, that would be useful to see just how it is related to the phono: If at all. The only valves that run with substantial heat are rectifiers & output valves.

More often than not when I find micro-phonic valves around the 2nd detector, (normally horrid little 6AV6's) it's a fault other than the valve.

If there has been previous tampering, check that valves wiring. I have no info as to that being the right valve. Pay attention to the heater pin socket wiring if they are on 2 & 7 and their is external shielding like a "goat": It's probably wrong.


 
 Return to top of page · Post #: 3 · Written at 12:19:08 AM on 12 May 2017.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 601

I seem to recall that the EBF35 has the same connections, but I could be wrong. And even if it did, there's no guarantee it would work.


 
 Return to top of page · Post #: 4 · Written at 8:13:25 AM on 12 May 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2626

Data can be downloaded from Franks electron tube pages if you have no info? http://www.tubedata.info/

EBF35 same pin out. Also remote cut-off pentode

Screen for 250V 100K series resistor. Pinouts same. I have a feeling I have one or two. Metalisation is the normal issue with any of that lot as pulling the tube out by the envelope can break the earth wire. I have repaired that & metalisation cab be replaced with conductive glue.

HRSA "Radio Waves" did publish an article I submitted doing that to an ECH35. As a successful experiment in saving it.

We do not condemn the old valve until proven faulty. If it has a cathode resistor there will be a voltage drop across it G1 -2V (Both) if it's conducting.

Even a dead oscillator will kill the radio section. Try an IF alignment & see if the signal gets through from the pentagrid. A transistor radio (at the right frequency) should pick up the oscillator.

Marc


 
 Return to top of page · Post #: 5 · Written at 6:13:07 PM on 12 May 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 478

The 6AR7 was an AWV design but, apart from the shorter envelope, very similar to the EBF35. They were promoted by AWV as being ideal for "reflexed" service, i.e. using the IF amplifier as as the 1st audio amp as well. A clever idea invented by Langford-Smith at AWA, it gave "5 valve" performance from 4 valves. It was first used in the Empire State radios to make a 5 valve radio with an RF stage.

Note that you will need to link pins 2 and 7 to use the EBF35, making sure that pin 2 isn't currently being used as a tie point. The 6AR7GT has G3 tied to K and connected to pin 7 with pin 2 as N/C If it is already connected to pin 7 you are laughing.

As Marcc said, the heater connections on both of these valves are unusual for octals, being pins 1 and 8. Normal Octal convention is heaters on 2 and 7.

6AR7s were only made by AWV in Australia and so will be hard to find internationally. I note my usual source has neither the 6AR7GT or the EBF35.

The 6B8GT has totally different pinouts.


 
 Return to top of page · Post #: 6 · Written at 9:01:51 PM on 12 May 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2626

AWA Valve manual shows EBF 35 & 6AR7 to be absolutely the same pin outs. It is pin interchangeable. But note the screen resistor.

I would still be inclined to do some checks before condemnation.

One of my tactics for lost signal in super-heterodyne sets is to use my semi permanent setup and feed in an IF signal at the Signal grid as per alignment. If it fails to materialise at the speaker, I can then use an oscilloscope to see where it got lost.

That, and an audio signal, injected at the volume control, (not cathode type) to ensure the audio is working (first step) normally pings the area of interest, swiftly.

I do enjoy the results of repair / refurbish but there is no difference in methodology here; All are done on the basis of a commercial refurbish, so dilly dallying looking for a fault is not on. There are procedures for finding faults quickly. This is one of them.

Marc


 
 Return to top of page · Post #: 7 · Written at 9:56:25 PM on 12 May 2017.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 601

EBF2G could also be considered as a replacement.


 
 Return to top of page · Post #: 8 · Written at 10:53:27 PM on 12 May 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2626

I have satisfied my curiosity: I went to look for an EBF35 & stopped looking after I tripped over a 6AR7. So via special adapter socket, home made, I stuck it in the the ancient VCT tester.

Now the heater is hard to see, so I stay with the ohm meter idea. If you turn off the light/s & close the door so the darkness can't get out. You look at around a 45degree angle into the envelope inside bottom across the top of the shield, you should see a reflection of the heater glow. Its only a pin point at the top.

Marc


 
 Return to top of page · Post #: 9 · Written at 10:58:07 PM on 12 May 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 3755

 
 Return to top of page · Post #: 10 · Written at 7:37:24 AM on 13 May 2017.
JFB's Gravatar
 JFB
 Location: Milton, NSW
 Member since 27 June 2016
 Member #: 1945
 Postcount: 13

A slightly dated copy of the Historical Radio Society of Australia's valve bank data shows that they have new and used 6ARTGTs in stock at somewhat better prices than above. Perhaps a good reason to join the society - see http://www.hrsa.asn.au/


 
 Return to top of page · Post #: 11 · Written at 5:51:37 PM on 13 May 2017.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 339

Yeah, I have found one for $24 free postage which is fairly reasonable, The Audio amplifier section is very good, I have new styli and use the turntable for my records. The 6AU6 was microphonic, so I put a NOS-NIB one in there, expecting that to work as physically the radio looks untouched inside, no evidence of anybody having ever had it apart. I'm going to have to invest in a signal generator and oscilloscope if I can find one working which doesn't cost an arm and leg, I'll just need to keep an eye out. I only suspected the valve as I couldn't see any light whatsoever and It was cold whereas the other tubes had slight warmth.


 
 Return to top of page · Post #: 12 · Written at 5:56:20 PM on 13 May 2017.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 339

Thank you all very much for your comments and links, very much appreciated. Cheers.


 
 Return to top of page · Post #: 13 · Written at 3:39:30 PM on 16 May 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 478

Marcc, look more carefully at the pinouts. The EBF35 is slightly different to the 6AR7. To use the EBF35 you WILL need to link pins 2 and 7.

The diagram is confusing,after having passed through several generations of photocopying. they do look the same at first glance. The Mullard manual confirms it.


 
 Return to top of page · Post #: 14 · Written at 6:44:10 PM on 19 May 2017.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 339

Well I'm happy to say, I received my valve (6AR7GT) today, was a bit dubious as the Bakelite bit underneath the base which correctly locates it in it's socket, was broken off, however after carefully examining the position of where the broken lug was, and the slot in the socket, I popped in the valve and when I turned on the radio, it burst into song! Yayyyyy!!!


 
 Return to top of page · Post #: 15 · Written at 7:13:39 PM on 19 May 2017.
Redxm's avatar
 Location: Tamworth, NSW
 Member since 6 April 2012
 Member #: 1126
 Postcount: 382

Good result. Smile


 
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