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Old 25th Jan 2016, 2:07 pm   #1
Geoff 555
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Default PZ30 failure Bush TV22.

Hello, bit of a 2part question for you please. Turned the 22 on and all was well, remarked to myself 'that is a much better picture than I remember.' Well that of course was asking for a swift kick in the pants. Just looked away for a minute and sensed that something was not right and the picture had dissapeared. No smoke,bang just gone. No EHT EY51 dead. PL38 with a slight blue tinge. In more hope than anything else put a new EY51 in, just the same - panic- oh gawd not the Transformer. Didn't have a PL38 and managed to find a second hand unknown PZ30, put that in and 'phew' problem solved.
Now the PZ30 didn't have that many hours on it, 20 approx. question is do they fail just like that or should I look for a deeper cause?
Part 2.
Could you kindly suggest where to get a PZ30 and a PL38 please. The chap I used to use has retired.
Thank you all.
All the best.
Cheers.
Geoff.
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Old 25th Jan 2016, 2:25 pm   #2
mark pirate
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Default Re: PZ30 failure.Bush TV22.

Sounds like you have been very lucky there, my TV22 did exactly the same thing, but sadly it was the LOPT.
I have now sent it off to be rewound.

I have managed to buy NOS PZ30's and PL38's from ebay at reasonable prices.
Some of the valve dealers are a bit on the dear side now!

LLJ always recommended TV22 owners to keep a spare PZ30 on hand.
They do seem to have a hard life in these sets.

Mark
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Old 25th Jan 2016, 3:31 pm   #3
Mike Phelan
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Default Re: PZ30 failure.Bush TV22.

In the late 1960s one of our rental customers had one of the few remaining TV22s and refused to change it.
The only field calls ever needed were an annual PZ30 and a twice-yearly PL38!
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Old 25th Jan 2016, 6:10 pm   #4
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Default Re: PZ30 failure.Bush TV22.

Quote:
The only field calls ever needed were an annual PZ30 and a twice-yearly PL38!
I have certainly had problems with PZ30's, but have yet to change a PL38.
Even after two years of regular use, my Pye D18T is still on both the PZ30 & PL38 that were in it before I restored it!

I have a total of 14 sets that use these valves, let's hope that supplies don't dry up or climb to the cost of certain audio valves.

Mark
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Old 25th Jan 2016, 6:17 pm   #5
Geoff 555
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Default Re: PZ30 failure.Bush TV22.

Hello Mark and Mike thank you for the replies. Dear old LLJ he is sadly missed. I will try e-bay again but I could only find a very second hand unknown PL38.
If no luck I will come back for a dealer link.
Thank you, I am keeping my fingers crossed about the LOPT and hoping it has not been damaged.
Cheers.
Geoff.
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Old 26th Jan 2016, 5:54 pm   #6
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Default Re: PZ30 failure Bush TV22.

Out of curiosity Geoff, was the PZ30 a NOS Mullard yellow label from around the 1963/4 era?
John.
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Old 27th Jan 2016, 10:58 am   #7
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Default Re: PZ30 failure Bush TV22.

The late production TV22 was supplied with a PL81 instead of the PL38.
This did necessitate the change of value of certain component values.
Also, a B9A valveholder and an adaptor plate.

DFWB.
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Old 27th Jan 2016, 1:07 pm   #8
Geoff 555
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Default Re: PZ30 failure Bush TV22.

Hello John. Hope you are well.
No not yellow, white writing with.
5K1
B9H
Just above the valve base. Bought 'NIB' done about 20 hours maximum. As a matter of interest would you happen to know what happens to them please?
All the best.
Cheers.
Geoff.
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Old 27th Jan 2016, 2:30 pm   #9
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Default Re: PZ30 failure Bush TV22.

I do have PZ30s and maybe PL38s but as I am on the other side (Dark Side ) of the world at the moment I'm not much help to you. Quality & quantity unknown.

Back in the UK late March if it helps.

PL36s any use? Got loads.
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Old 27th Jan 2016, 3:31 pm   #10
Geoff 555
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Default Re: PZ30 failure Bush TV22.

Hello BOATER SAM thank you for the message it is much appreciated. To be honest I would really like NOS valves because expensive they may be but a damaged LOTX etc, would be not good, it seems that they have a relatively short life in the 22 so it seems.
Cheers.
Geoff.
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Old 27th Jan 2016, 3:40 pm   #11
Geoff 555
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Default Re: PZ30 failure Bush TV22.

OK chaps I am having the usual luck searching IE. not a lot. Although listed by certain sites as having some then it's a different when checked.
So would you be so kind please point me in the right direction of a supplier for new PZ30's and PL38's.
Where have all the suppliers gone, tried 3 I used to use and they have packed up.
Thank you.
Cheers.
Geoff.
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Old 27th Jan 2016, 5:13 pm   #12
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Default Re: PZ30 failure Bush TV22.

Hi Geoff

Have you tried Langrex? Both valves are on their stock list. I got a quote from them recently for a rectifier and it was very reasonable.

http://www.langrex.co.uk/stocklist.html
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Old 27th Jan 2016, 5:48 pm   #13
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Default Re: PZ30 failure Bush TV22.

There are 4 PZ30 for sale on ebay now, Malc.
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Old 27th Jan 2016, 6:40 pm   #14
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Default Re: PZ30 failure Bush TV22.

I've found a PZ30 here in the shop. I can try it out in a TV22 to find out if is any good. You can have it FOC, kostenlos. Just pay for the postage.

DFWB.
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Old 27th Jan 2016, 6:58 pm   #15
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Default Re: PZ30 failure Bush TV22.

The PZ30 is OK.

DFWB.
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Old 27th Jan 2016, 9:30 pm   #16
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Default Re: PZ30 failure Bush TV22.

Geoff, you asked if failure after 20 hours indicates a problem.

The PZ30 has two independant diodes in the envelope.

If it is wired as the mains rectifier, the valve sockets need to have cathode1 wired to cathode2 and the anode1 wired to anode2.

If you have dry joints or missing wires the valve will be over run.

Has the reservoir capacitance limit been exceeded?
Does it have sufficient series resistance?
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Old 27th Jan 2016, 9:35 pm   #17
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Default Re: PZ30 failure Bush TV22.

In the TV22 it appears that one diode in the PZ30 is the mains rectifier, the other is the booster diode in the line output stage.
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Old 27th Jan 2016, 9:50 pm   #18
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Default Re: PZ30 failure Bush TV22.

Read about the PZ30 here: http://www.r-type.org/exhib/aaa0498.htm

The PZ30 developer was Mullard.

DFWB.
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Old 27th Jan 2016, 10:31 pm   #19
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Default Re: PZ30 failure Bush TV22.

You could try a 180 ohm, 25 watt resistor (52 V @ 0.3 A) and a couple of ultra-fast 4007 diodes ..... Make sure at least the boost diode is the UF version, which usually have the cathode band made out of rows of separate little squares as opposed to solid silver.
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Old 27th Jan 2016, 11:26 pm   #20
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Default Re: PZ30 failure Bush TV22.

The British designed Mullard PZ30 started life in 1949 with a bad record. As mentioned they were often employed as boost diode and H.T. rectifier in a similar arrangement to the Mazda U801 in 12" receivers. The first receiver to use it was the PYE B18T closely followed by the Bush TV12. Unfortunately for PYE being the first off the mark they suffered problems with the PZ30 more than Bush and to no fault of their own.
The early versions with the perforated anodes used to blow up with a shower of sparks blowing the mains fuse. Mullard modified the valve and considerably improved its reliability to the extent that replacement became a much rarer necessity.
I have several completely useless NOS yellow label PZ30's that went S/C after a few hours use blowing the surge limiters in two separate Pye B18Ts. What is it about these yellow label valves?
Most PZ30s that are around these days have stood the test of time and appear to be completely reliable.
As far as the PL38 is concerned, I cannot remember ever having replaced one. They are a very rugged valve like the 6.3v version the EL38.
I have also had the odd PZ30 go O/C internally probably disconnecting the cathode connection. I have a number of used ones that look terrible! Black and with burnt areas above the heaters deposited on the glass and they rattle.
They work 100% ! You can't win.
Compared with the U801 it is good valve. The early versions of the later PY32 suffered like the PZ30 but all these problems were completely sorted out by the PY33, the replacement for all versions of the PY32.
Probably the best rectifier was the little B9A PY82 often employed in pairs. Very reliable and they never appear to go low emission.
I have a black museum of PZ30s. I will attempt to picture them tomorrow. John.
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