Mullard high speed tester

[andrew_whitham]

HI ervington,

How did you get in with this? DID you get a manual with it?

I recently got a Mullard high speed valve tester and am in the process of giving it a re-furb

I think that so long as the transformers haven't quit it "should" be repairable.

If they havent been replaced then the caps are perhaps your next biggest source of headaches?

Andy

[andrew_whitham]

Yeah ok the meter... good point, well made

failing that the caps.. turns out the problem on mine is (95%) the reservoir cap on the CRT circuit

This is a 1951 bit of kit, every resistor was within tol...

as it turns out the DCR of the cap was too low and the differential amp was getting all bewildered

Now does anyone know where you might get a 16 + 16 uf 500v cap?

The schematic of my tester is attached (mods permitting - I didn't draw this one) I didnt think it was THAT simple
(and you are missing the card reader section)

Andy

[EC8010]

I don't suppose you could send me a higher resolution scan of that circuit could you?

[andrew_whitham]

Drop me a mail and I'd be glad to and the manual too, I'm scanning it, because electrons weigh less than paper

For one I would be glad of any advice regarding the power supply for the HT I have studiously ignored valve rectified supplies and I'm aware I'm (again) not completely competant.

Andy

[EC8010]

There should be a mail on its way...

[andrew_whitham]

Originally posted by EC8010
There should be a mail on its way...

I messed up and deleted it, then I used several rude words... computers eh? supposed to be idiot proof

BTW I followed your statement about the HT regulator I have some NOS 6AS7G's that I want to use SOMEWHERE... But in this case I'm wondering about replacing the HT rectifier (a FW4-500) with a S/S equivalent. shoudn't do any harm?

Will anyone get upset if I post a rapidshare link to the schematic on here? Sending 3.5Mb emails from China is "problematic" but that seems to work fine. (no I dont know why either. )

Andy

[EC8010]

You will get a higher HT voltage with a silicon rectifier than valve. Voltage drop across a valve can easily be 15V or so.

[andrew_whitham]

ok, for the benefit of anyone apart from EC8010 and me

it seems that a discussion about the vagaries of my tube taester is unlikely to be useful to the thread starter ervington beyond "check your component values"

As a result I'll do the decent thing and slope off into another thread... I have questions that will only dilute this one which isnt supposed to be the idea...

Andy

[EC8010]

OK, I can take a hint. I have split the thread...

[andrew_whitham]

but thanks...

If there IS more than one of these still going, this forum is probably one of the places its owner visits... (hopefully)

If there are no objections the full schematic is at http://rapidshare.com/files/18662704/testerb.jpg.html

if anyone is interested enough to aquire the full manual drop me a mail. I'll forward the link...

Ok so here is where I am at at the moment:

1951 caps are dead.
Replacing caps. Some of these are so leaky they prevent operation, ie it works better with them diconnected. a good reason to suspect the rest will be a bit dodgy.
Can anyone suggest a good sourse of 16uF / 500v Caps the original is a 16+16u 500v electrolytic from TCI its not the most standard of components now. And to think my wicked silicon ways nean I have several 390uF caps that are rated in my store - this is where my efforts are at the moment

Tubes last longer than you think.
I replaced all the tubes except for the ridiculously expensive EL37 and the FW4-500 no real effect, but I proved to myself that the EZ35 and the ECC35 in the schematic can be replaced with UX4 and 6SL7 respectively. I suspect the EL37 is on its way, popping it into my EL34 / KT88 amp did not yield pleasant (audio) results Putting a KT88 in the valve tester however seems to give the same voltages - am I missing a trick?

missing cards:
the only card of note I dont have is "card 1059" (i Think) for the ECC88 series of tubes! Its a good job NO-ONE uses those . Can anyone provide me with the details? this is an achilles heel of this type of tester - not simple to figure this out yerself unless you have the card for your tube.

Any advice on making this into a useful instrument is gratefully received - what else might be failing after all this time?. The calibration procedure I think is in the manual! so close is going to give sensible results I think

Andy