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Old 3rd Sep 2019, 7:34 pm   #21
G6Tanuki
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Default Re: Bush SUG26

Or could the short one be an EZ41?

http://www.r-type.org/exhib/aaa0126.htm

The EZ41 was well-used in smaller/cheaper 5-valve broadcast receivers like the Pye P75.
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Old 3rd Sep 2019, 7:44 pm   #22
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Default Re: Bush SUG26

I'd wondered if the "Tungsram EZ40" in the pic was a creatively-relabelled EZ41, but taking a closer look reveals it toi have the inter-leaved cruciform anodes like the familiar and later EZ80, resulting in a lower electrode assembly height than the taller specimen with its separated and stacked anodes. It might even be later, legacy-support production using an EZ80 assembly on a B8a base- that would sort of make sense with similar heater currents and other ratings.
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Old 3rd Sep 2019, 7:46 pm   #23
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Default Re: Bush SUG26

A Philips one:

http://www.r-type.org/exhib/acd0003.htm

Lawrence.
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Old 3rd Sep 2019, 10:33 pm   #24
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Default Re: Bush SUG26

Hi Robert, replacing the rectifier seems to have been a good move and a step forward. As far as the hum and squealing as you tune across the band is concerned, does this noise still occur when switched to gram? If not then if you touch the blade of a screwdriver and apply the tip to the gram socket you should hear a healthy hum that gets louder as you advance the volume control. That would at least indicate that the audio amplifier section is working reasonably well. You say you have replaced all the wax capacitors but look out for any small brown or black "Hunts" capacitors which can also cause trouble, particularly when used as screen grid decouplers. The only other thing I can suggest is to give the wavechange switch contacts a good blast of switch cleaner and also carefully clean the valve pins and sockets. Wiggling the valves can also often reveal loose or broken socket receptacles but don't try that with the rectifier or output valves as they get extremely hot. Cheers, Jerry
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Old 4th Sep 2019, 8:29 am   #25
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Default Re: Bush SUG26

The higher than expected voltages may be due to the type of voltmeter used.

The older moving coil meters loaded the circuit and dragged the voltage down to the values shown on the trader sheet.

The real operating voltage can only be found if the test meter does not take any current from the circuit.

DVM's typically have input resistances of 1M and 10M Ohms and will give voltage readings higher than that stated on the Trader sheets.
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Old 4th Sep 2019, 9:34 am   #26
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Default Re: Bush SUG26

Also worth measuring the cathode voltages and comparing to the service sheet. The high anode voltages on both EBC41 could be an indication of no/very low emission. Cheers, Jerry
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Old 4th Sep 2019, 9:54 am   #27
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Default Re: Bush SUG26

I have very low voltages on V3 and V4

V3 pin 1 = 5.7v, pin 2 = 112v, pin 3 = 0v, pin 4 = .2v, pin 5 = .4v, pin 6 = 0v, pin 7 =.4v
V4 pin 1 = 5.7v, pin 2 = 121v, pin 3, 4, 5, 6 and 7 = 0v

Would this indicate faulty valves.
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Old 4th Sep 2019, 10:37 am   #28
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Default Re: Bush SUG26

According to your measurements there is no voltage on the cathode of V4 but the voltage on the anode of V4 suggests that the triode section is drawing current, you need to investigate as to why that should be.

Lawrence.
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Old 4th Sep 2019, 11:48 am   #29
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Default Re: Bush SUG26

Hi Robert, V3 is possibly low emission - in view of the fact that the cathode voltage is 0.4v in lieu of the expected 1.0v. In other words the anode current is only just over 0.1mA compared to the expected 0.3mA. However, it should still work. Maybe worth checking that its cathode resistor R18 (3.3k) hasn't gone high which wouldn't help if that's the case. As Lawrence says V4 appears to be drawing some current as there is a voltage drop of some 18v across its anode load resistor R21 (68k) indicating an anode current of about 0.3mA instead of the expected 1mA. You should also have some voltage on the cathode of V4 (up to 0.8v) not zero. The only other explanation for the voltage drop across R21 is if C30 (0.01uF) is leaking. Did you replace it? You could try swapping the two EBC41s around and then see if the cathode voltage at V4 has changed. P.S. did you try the buzz check while switched to gram that I suggested? Cheers, Jerry
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Old 4th Sep 2019, 10:44 pm   #30
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Default Re: Bush SUG26

Hi Gerry, I did the screwdriver test on the team and I could head the hum while I turned up the volume.
R21 the 68k was reading 88k so I replaced it.

I swapped the 2 EBC41 valves and measured the voltages.

V3. Pin2 = 134v. Pin3 = .09v. Pin4 = 0v. Pin5 = .9v. Pin6 = 3.7v. Pin7 = 1.02v
V4. Pin2 = 153v. Pin3,4,5,6,7 = 0v
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Old 5th Sep 2019, 9:13 am   #31
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Default Re: Bush SUG26

Hi Robert, thanks for the info. I think there might be something wrong with the V4 valve socket. With the valves swapped over it looks like the EBC41 now in the V4 position is not conducting because the anode voltage is much too high and the cathode should be above zero volts, whereas it appeared to be conducting when it was in the V3 position. Vice versa the valve now in the V3 position appears to be working OK. On reflection the screwdriver test will provide a hum even if only half the push-pull pair is working - if V4 is not conduction you will get no output from V6 but V5 will still provide output to the speaker. I'm thinking you might have a broken pin socket in the V4 valve holder. With power off try removing the valve then wrap some stiff wire round one of your meter probes and prod the wire into each pin socket in turn and check continuity to the solder tag underneath.
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Old 5th Sep 2019, 9:15 am   #32
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Default Re: Bush SUG26

Hi Gerry, I had replaced C30 when I did the original wax cap replacements.
On V4 pins 4,5 and 6 are linked together and grounded.
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Old 5th Sep 2019, 11:51 am   #33
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Default Re: Bush SUG26

Broken pin sockets in these rimlock holders are very common, had this problem on an AC34 recently and the DAC10 I'm currently doing, usually one of the two splines has broken off so the socket does not grip the pin, if you tease the pin sockets with a sewing needle you can find where the problem lies. There are usually unused pin sockets on the rectifier holder that can be used as a replacement
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Old 5th Sep 2019, 2:02 pm   #34
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Default Re: Bush SUG26

Hi Robert, OK, understood. Agreed you don't need to worry about V4 pins 4, 5 and 6. Pin 7 is the cathode of V4 and should be grounded via R22, a 2.2k resistor. Therefore if the valve is passing current there should be a voltage across R22. The other thing that can happen, even if a pin socket isn't broken as electrogram says, is that you have a high resistance (or a broken pin socket) on the heater pins (1 & 8). Can you tell if V4 is lighting up? If so, then either pin 2 (anode) or pin 7 of the socket must be dodgy. Good luck - perseverance pays off in the end! Cheers, Jerry
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Old 5th Sep 2019, 9:51 pm   #35
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Default Re: Bush SUG26

Hi, I checked the pins of V4 and the continuity wasn't great on pin7. I pushed a stiff wire in and out a few times on all the pins.
Continuity is much better now.
V4 is lighting up.
I am now getting 102v on anode and 1.2 on cathode.

I have taken out all the valves and cleaned and tested all the pins.
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Old 5th Sep 2019, 10:45 pm   #36
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Default Re: Bush SUG26

That sounds better. If you have an audio source such as ipod/phone then select gram and feed in some music into the gram sockets. You might need to play about with the volume of the audio source. The radio is then just being used as an AF amplifier and if the sound is clear and undistorted then hopefully the AF stages are now good. Are you still getting the squealing noise when switched to radio? Do you have an aerial wire plugged into the radio? Cheers, Jerry
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Old 6th Sep 2019, 4:32 am   #37
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Default Re: Bush SUG26

Hi!

The valve you show in your pic is an EZ40, just very low emission!

Make sure you haven't got any broken valve–holder contacts on the ECH42 and EF41 bases!

The EF41 pin data is a bit inconsistent, Mullard give pins 3 ans 4 as "i.c" (internally connected) with pin 7 as "k, g3" whereas some of the lists of valve pinouts in the older R & TV Reference books state that pins 3 and 4 are also cathode and g3 – not always the case, some Mullard EF41 valves I've seen have only short unconnected stubs leading from 3 & 4.

(The EF41 has an internally connected suppressor grid (g3) which should be common to the internal screening of the valve and it's cathode on pin 7).

The symptoms suggest you might have i.f. instability, which may be caused by one or more of the screen–grid or bypass capacitors on pin 5 (screen grids) and pin 7 (cathodes) of the first valves going open–circuit, or alternatively an open–circuit a.g.c. line decoupler.

(I haven't got an SUG 26 circuit handy to quote the circuit reference numbers from I'm afraid!)

I would locate the screen–grid bypass, cathode–bypass and a.g.c. line decoupling capacitors and try replacing all these as a next step – there wouldn't be more than 5 I should think, or less if the ECH42 and EF41 screen–grids are common, which could be the case!

If replacing the bypass capacitors doesn't help, check the values of the oscillator triode anode and grid leak resistors for the ECH42 triode section – a high–resistance one will cause the oscillator to "block" or "squegg" which will cause all sorts of strange noises!

Finally make sure the frame of the tuning gang capacitor is reliabily earthed to chassis, and that any rubber mountings it's mounted on aren't hardened or perished, as this can also be a cause of instability or microphony!

There is the possibility of "microphonic" valves in the early stages of the set, but my experience of the Mullard '40 series is that it's very rare – the '40 series are fairly robust and reliable valves, and the only failure I had was a defective EBC41 cauaing no sound in a Pye Fenman II!

Chris Williams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

Last edited by Chris55000; 6th Sep 2019 at 4:53 am.
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Old 8th Sep 2019, 4:56 pm   #38
RobertF
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Default Re: Bush SUG26

Hi,
I have made a lead and connected a phone to the gram socket.
I am getting perfect sound through the gram socket.

The tuning capacitor is well earthed.
The rubber mountings look good.
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Old 9th Sep 2019, 8:11 am   #39
cathoderay57
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Default Re: Bush SUG26

Hi Robert, nice work, well done. Is it still squawking on all bands on radio? Cheers, Jerry
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Old 9th Sep 2019, 8:42 am   #40
RobertF
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Default Re: Bush SUG26

Hi Jerry,
I am only getting a bit of a whistle at one point on the tuning scale. I don't know what frequency it is at as I have everything out of the cabinet. It is about 1/4 way across from the left.
The rest of the scale is quiet.
Regards

Robert
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