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Old 23rd Mar 2010, 9:36 pm   #1
Al-wood
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Default Michaelson and Austin TVA 1 Bias Help

Hi
I have acquired a Michaelson and Austin TVA 1 Valve power amp and wonder
if there is anyone of you in the West Yorkshire area who can set the bias on this amp for me ?
I have no equipment or knowledge of how to do this, and have been trying through research on the net to get a better understanding of what I have got and how to maintain it. I can travel with amp, I am based in Huddersfield.
Any help or pointers would be greatly appreciated

Am very happy to pay for the work doing the way.

Many Thanks in advance.

Regards,
Allan
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Old 19th Oct 2011, 4:06 pm   #2
leakstereo20
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Question Tva-1

HI Allan,

I own a very good looking Michaelson & Austin TVA-1 no. 553, an erly model. A lot of soldering jobs inside made it impossible for me to figure out the original hardwiring as far as the ground connections was concerned. I could not see where the chassis connection originally was located...was it close to the RCA screen's behind the driverboard...or close to the large PSU capacitors...did M&A make floating ground...no? There must have been a central ground point (starground) ? Could you show me pictures of the TVA-1 groundwires ( normally black wires)?

If you ( or someone in this forum) could help me on this one, by looking at your own TVA-1, I could advice you the bias for your TVA-1 / (Mentmore) depending on the cathode resistor, and also one way to keep your KT88's alive a little longer by change of the resistance between the signal screen of the KT88's to ground.

I look forward to hear from you.

Kim, Denmark
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Old 20th Oct 2011, 10:41 am   #3
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Default Re: Michaelson and Austin TVA 1 Bias Help

The TVA1 was a bit of a beast when new. Some blew up into flames, others were rather crudely made and difficult to fix (I'm being polite here). Late ones had the valves thrashed to increase power output and as the power went up, so did the fatiguing harshness missing in early ones..

There are a few people skilled in valve amp restoration around, a couple being Tube Distinctions (not cheap, but this chap makes some pretty devastating new stuff - his "copper" amps are the stuff of legend :lol and Glenn Croft, who, as well as making his own wonderful and less expensive products, does look at other valve gear, as well as his old models from twenty or more years ago.

If the TVA1 can be restored back to the core product as designed originally, it'll be very good indeed, but it depends how much tinkering was done in the manufacture of your sample, as well as the subsequent state of the capacitors and valves themselves.

Apologies for being so negative here, but I remember us being a dealer for them at the time. You may just need more than setting the bias now these are thirty plus years old.........

http://www.tubedistinctions.co.uk/custom.htm

http://www.croftacoustics.co.uk/products.html
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Old 20th Oct 2011, 12:21 pm   #4
leakstereo20
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Default Re: Michaelson and Austin TVA 1 Bias Help

As I am admirer of british hifi, I have to say that the two Michaelson and Austin TVA-1 valveamplifiers I heard over a pair of AR3a and AR11 sounded beautiful with very wide soundstage and no harchness at all.
One have to remember that the original TdP design and resistor values was based upon the MOV KT88's which could handle more mA and higher resistance between the signal screen and ground. The reissue KT88's of today requires more attention as far as screen to ground resistance is concerned.
The mentioned problem of the reissue KT88's that "runs with bias" and as result burning flames from overheated wirewound resistors, is located to the fact, that the resistor value from input screen to ground must not exeed 145kOhm.
The TdP TVA-1 design is very good( one of the best in my opinion) and the Partridge OP's sounds great, but we have to adjust some resistor values to the available valves of today. Find some TVA-1 information at the link below.

My problem is to find a Michaelson and Austin admirer that own the TVA-1, and that someone do have the time to handdraw the original ground wiring and send it to me.
In return I have some information for several amplifiers at my amateur non-payment site called: www.tubeamp.hobbysider.dk

Leak-Luxman-Mosfet PA100 ect. This is help to repair the amplifiers - not advertisement!

Rgds
Kim

Last edited by Brian R Pateman; 20th Oct 2011 at 12:55 pm. Reason: Quote of preceding post is not required. Try "Post Reply" instead.
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Old 20th Oct 2011, 3:36 pm   #5
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Default Re: Michaelson and Austin TVA 1 Bias Help

Really nice and well built amplifiers from mr. Anthony Matthews...especially the crome-steel 30watt valveamp. I did not notice his amplifiers before.

thanks, Kim
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Old 21st Oct 2011, 1:14 pm   #6
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Default Re: Michaelson and Austin TVA 1 Bias Help

Hi Dave,

Erlier I spoke with the former UK distributor of Mentmore products, Colin. Unfortunately he did'nt know that much about the technical stuf inside valveamplifiers.
Colin mentioned the same points as you did, that the TVA-1 was "eating valves" and something about flames comming out.
As I am not educated within valveamplifiers, a lot of reading time was used in the Danish Technical School for engineers, DIA, old library.

10 years ago I used the TVA-1 circuit in a DIY project, where I tried with used EL34's in the setup. The experience was heavily burned cathode resistors. At that time I did not find, what caused the "runaway bias". Fortunately I found some guys with the same valve interest and we discovered some of the secrets from this TdP circuit.
This erly Tim de Paravicini design easy equals modern valveamplifiers and , In my opinion ,with better sound ...of cource with the right resistor values and new signal capacitors.
Nothing is free... the nature laws has limits, and I think to remember the -3dB for the TVA-1 Partridge OP's to be approx. 38kHz. But what a thunder bottom and musicality!
Then you mentioned the TVA-1 built quality. Yes - some parts could have been selected from better suppliers like the powerswitch a.o., but the 2 mm thick polished steel chassis was very well suited as base for the heavy transformers. But in all ...better than most far east replica amplifiers, I would say.

My DIY Leak Stereo 50 with exact winding by winding copy of the original OP's was messured to approx. 56kHz -3dB and below 10Hz ...showed by the old Brüel and Kjær equipment.

If you are aware of any people in UK that have the same passion for Michaelson and Austin valveamplifiers, then please let me know. There have to be someone in UK?

Kind regards
Kim
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Old 21st Oct 2011, 9:35 pm   #7
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Default Re: Michaelson and Austin TVA 1 Bias Help

I'm well out of the industry now, but I do have a good mate with something of a vintage "museum" of assorted stuff. sadly, a TVA1 doesn't feature - and probably won't to be honest... he does have a lovely Stereo 20 though, and some modern EAR amps, the former of which recently serviced to a high standard, and that's one funky little power amp - huge fun :lol:

I'll stick to my re-built Quad II's thanks
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Old 22nd Oct 2011, 10:42 am   #8
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Default Re: Michaelson and Austin TVA 1 Bias Help

Ok, thanks for your thoughts about the TVA-1....Anyway...I suppose that we have to wait and see if other members of Vintage-Radio.net comes up with additional information to the TVA-1 groundwiring.
I know a handdrawing takes a while, but closeup bottom pictures of the TVA-1 might do it.
Good luck with the Quad II's and the re-bulit. Good looking , well sounding valveamps. Mr. Peter Walker's Quad II 1959 design...4 valves 8 resistors 4 capacitors for the amplier part with an ekstra cathode feedback winding...without being an expert...this was simple and intelligent! Very difficult to make an DIY copy of the Quad II amplifier OP's.

Rgds.
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Old 22nd Oct 2011, 2:25 pm   #9
robin coleman
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Default Re: Michaelson and Austin TVA 1 Bias Help

The mentmore and Quad amplifiers were made by a company called Papworth Audio Technology who I worked for when Papworth Industries was about.

I worked for them and sorted out all the Mentmore stock. The owner was Eddie Fincham. A shop in Cambridge called Audiophile might be able to tell you if they still exist.

Last edited by Darren-UK; 29th Oct 2011 at 11:01 am. Reason: GI.
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Old 22nd Oct 2011, 3:33 pm   #10
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Default Re: Michaelson and Austin TVA 1 Bias Help

The story as I understood Colin was that when M&A went broke they sold the company to Mentmore which included Tim's design TVA-1 and TVA-10...he was not sure, but the M100 should have been designed at this point.
After this Papworth Group took over and bought all, and with Mr. Eddie Fincham in charge they produced:

TVA-10 50/50 EL34, M100,M200,M300 and more...

I have already tried to get some information from Papworth Group without any luck. I may try the Audiophile shop in Cambridge as you suggest....but its "a long road" just for some information regarding groundwiring I think. Another guy with interest in M&A and the TVA-1 seems more likely the way.

rgds.
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Old 22nd Oct 2011, 5:54 pm   #11
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Default Re: Michaelson and Austin TVA 1 Bias Help

The Quad 2 was gold plated by a company that does Viners cutlery. All the early Mentmore cables were done in a samon pink cableform horrible to make and wire. The PAT ones were a bit better. I spent a few years making them and hours assembling the fins for the TVA50 after Eddie bought the company from Papworth. He made them from his home in Cambridge and exibited them at the Penta exhibition. Haven't come across an M100 yet, I will do one day, maybe they appear on eBay?
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Old 23rd Oct 2011, 10:38 am   #12
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Default Re: Michaelson and Austin TVA 1 Bias Help

Robin, Not quite sure what "samon pink cableform" is? ..something like a wire-bakery ...and yes..the chassis goldplate on the Quad II looks pretty nice IMO.
But one thing inside the TVA-1 and later Mentmore I have been wondering about... why did they use that thick isolating plasticmaterial in all the hardwiring? Hard to bend and form the wires, and even more difficult to repair after 20 years.
If you did solder the "pat" ones ..do you mean Papworth..then you might remember the "original" way of ground wiring?
"Effie"... is it mr. Eddie Fincham? The story is that mr. Fincham bought the rights to produce the M50,M100 aso.?
While you read this have in mind that english is my second language.. "the penta exhibition" ..I guess its a hi-fi forum for the new/latest/best amplifiers , which I have never heard about.
Hobe that you find the M100 some day. Less than 6 month ago the M100 was offered in DK. I shall remember you if the M100 turns up ones more. A guy in Denmark/Fyn offers at the moment two M200's but the saleprice seems a bit high I think. He offers trade as well. A bit heavy 70Kg. Look at hifi4all.dk

rgds

Last edited by leakstereo20; 23rd Oct 2011 at 10:47 am.
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Old 23rd Oct 2011, 1:16 pm   #13
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Default Re: Michaelson and Austin TVA 1 Bias Help

Quote:
Originally Posted by robin coleman View Post
havent come across a m1oo yet i will do 1 day maybe they get on e bay
Can't find the M100's for sale, but I found some nice pictures in Italy:


http://digilander.libero.it/pasqua49...re%20M-100.htm
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Old 23rd Oct 2011, 3:27 pm   #14
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Default Re: Michaelson and Austin TVA 1 Bias Help

Have received some help from a TVA 1 owner...looks like Mentmore because of the laquered driverboard...later model.

The schematic shows chassis ground close to the large psu capacitors. Could anyone confirm that the starground point is situated below the bias pcb-board? ..impossible to see on the attached picture.
The RCA input connectors isolated from chassis.

Looking at the picture it looks like the KT88 cathode resistor wires has been soldered up upon the groundplane on the driverboard?
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Old 23rd Oct 2011, 9:00 pm   #15
robin coleman
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Default Re: Michaelson and Austin TVA 1 Bias Help

Yes the grounding point is where you say. We also used to have a nut insert in the stainless steel chassis or sometimes usde the transformer retaining nuts. PAT stood for Papworth Audio Technology. The one in the picture is one I wired, I recognise my wiring. Salmon pink was a light pink cable RS used to sell.

When we cleared the Mentmore factory we had lots of half built units which we either rebuilt and repolished the stainles steel while we were waiting for new chassis to be made. We used various cables for the hard wiring links in Hellerman sleeving and some old cable that Eddie Fincham had aquired from his days at Pye and Philips. Audio screened cable was gold cable Kelvin K2 type Transformers were sprayed as and when we wanted them. Penta was a HiFi exhibition. As a note we put odd coins in the transformers when we potted them as a sort of time capsule. Do you have any top views?

Last edited by Darren-UK; 29th Oct 2011 at 11:02 am. Reason: GI.
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Old 23rd Oct 2011, 9:05 pm   #16
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Default Re: Michaelson and Austin TVA 1 Bias Help

As another note, when Papworth was built them I was one of only three people who ever made them. I have looked at the photos and recognised my build label on it. How spooky! May have to hunt one down.
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Old 23rd Oct 2011, 10:11 pm   #17
leakstereo20
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Default Re: Michaelson and Austin TVA 1 Bias Help

Thank you Robin,
I think this is getting more and more interesting! I joined this forum last week and wished that someone could tell me more about Michaelson & Austin / Mentmore / Papworth and here you are.

I have made several DIY valveamps...all with central ground-points close to the main psu capacitors. On the TVA-1 I bought, someone has drilled a hole in between the two KT88's placed close to the driverboard...far away from the power-capacitors, but I could not figure out whether this was the original ground-spot? ...now I know! I believe that the distance from this central point in the middle of the chassis to the capacitors causes the weak 50-60Hz hum!
The light pink cable from RS is very thick...I understand why you found the wiring difficult. The cable Eddie Fincham had aquired from PYE must have been easyer to hardwire, because the isolation was a bit thinner? Funny with the coins when you potted the transformers.
Yes.. I have some pictures....please find them attached.

You must have done things well in Papworth...the guy I received the pictures from said, that the basic wiring inside looked very professional, but the former owner ,before my italian friend bought the amp, made a terrible soldering job. He has re-built the amp and the amplifier should be close to your factory standard now, exept from the small delay relay pcb section bought in USA.
I shall not complain...the built lable inside my TVA-1 serial no.553 shows...(Kevin Austin) Kevin/OK sep.1979...and the basic soldering work still looks fine after 32 years!

Yes.. its odd that your work returns to you after 25-30 years.

I may have some few additional questions later ....I promise not to take too much of your time

Best regards
Kim
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Last edited by leakstereo20; 23rd Oct 2011 at 10:24 pm.
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Old 24th Oct 2011, 3:48 pm   #18
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Default Re: Michaelson and Austin TVA 1 Bias Help

Since yesterday I thought....What about a collection or gathering of Michaelson & Austin/Mentmore / Papworth /TVA-1/M100 information here in this forum? We might even get a permanent page if we speak kindly to the Master moderator here

For almost two years I have tried to find any TVA-1 documentation without luck...and I know several people in the same situation, and for that reason I made an attempt to messure my own M&A valveamp from scratch.

I found some japanese guys doing great re-built work at:

http://amp8.com/vv-amp/michaell/tva-1-2.htm
http://amp8.com/vv-amp/michaell/tva-1-7.htm
http://amp8.com/vv-amp/michaell/tva-1-4.htm
http://amp8.org/vv-amp/michaell/tva-1-5.htm
http://topseller.jp/store/member/amp...ll/tva-1-6.htm

I tried to contact hifi.do.japan...no answer!

Even if I got the pictures above on my PC, I am not allowed to show them to you because of copyright.

Unfortunately my japanese is not "perfect", and the Google translation do have several limitations.
I might have some drawings supposed to be original from M&A and a TVA-1 test from Sweden.

I try to start with the M&A TVA-1 drawing... and responce would be most welcome.

Picture 1 should be original. Picture 2 converted to fax copy.

Pic. 3 PSU in grey dark copy. pic. 4 amp. in grey dark copy for better contrast.

Its obvious that the "original" TVA-1 drawing is not clear enough (nomally approx 2,2Mb), and post me for a copy.

Note that the bias resistor of 220K need to redused by use of old and used valves! 100K in this position together with 20K pot and approx. 39K to ground. To be showed on the next post.

rgds.
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Last edited by leakstereo20; 24th Oct 2011 at 3:55 pm.
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Old 24th Oct 2011, 5:18 pm   #19
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Default Re: Michaelson and Austin TVA 1 Bias Help

For the above TVA-1 Michaelson and Austin "original drawing" see Picasa Web for details 2,21Mb :

https://picasaweb.google.com/1031761...91698864037250

Use the magnification button at Picasa.
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Old 24th Oct 2011, 5:29 pm   #20
tri-comp
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Default Re: Michaelson and Austin TVA 1 Bias Help

Allan,

This is indeed a VERY nice amplifier.
For others, go have a look here:
http://amp8.com/vv-amp/michaell/tva-1-4.htm
As you will see (more or less... you can always do a Google-translation for what it's worth) it should be considered doing a capacitor-job besides the bias-setting at the very least.

If/when you find someone willing to do the bias-job he should either know from a detailled service-manual what is the required cathode-current of the KT88's OR he could do an estimate with just the schematics on hand.
That's why I attach it here...

EDIT: One more place to go: http://www.jogis-roehrenbude.de/Roeh...VA-1/TVA-1.htm

Good luck,

/tri-comp
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Last edited by tri-comp; 24th Oct 2011 at 5:32 pm. Reason: EDIT: Found a German site as well...
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