G'day all

I got a little nipper..like this one
http://www.radiomuseum.org/r/hismasters_little_nipper_62_52_ch_62.html?language_id=2.

Seems sadly I got the one of many with a blown output transformer....primary open circuit by the looks of it
It is one of the black dipped ones yes...which Marc had said in another post, has a high "be dead" rate..ok in a much more eloquent correct term

It uses a 6X4 Rectifier and a 6M5 output tube (I have read of not so good things with the 6M5...anyway)

So my question is, Does anyone know what the specs are as in output impedances of the output Transformer

Sadly here they cost arms and legs but if I can find a suitable Hammond etc I might see if I can retro fit that

if someones got some info on its details it would be useful ..or even a possible replacement to get

other wise I guess I'll have to research the design to figure out what impedance it might be with a 6M5 in SE mode

Any help much appreciated

Thank you all

The 6M5 specs show a load resistance of 7k. If you measure the DC resistance of the speaker and multiply that by 1.3 you'll be close to its impedance. From that you can easily work out what transformer you need.

Antique Electronic Supply in the US keeps a good range of OP transformers at reasonable prices. I've bought from them before and their freight prices are not too high. The range is always changing and I don't see a suitable one at the moment but there's a couple that are close. Their categories are a bit unreliable and you won't necessarily see all the OP transformers under that category.

https://www.tubesandmore.com/products/transformers_chokes.

I've yet to find a 6M5 in a radio that wasn't dodgy. Replacements can be hard to find but there's threads on this forum about substituting other valves. I find the easiest is a 6BQ5, it might be just me but I find the sound from a 6BQ5 is much harsher than a 6M5 but quite acceptable.

They must have used those transformers in Kriesler as well. My statistic was that around two in eight of them had a good OP transformer.

I had a set in about six weeks ago that had a universal type that came from RS components, I think? It came with the problem set, but was a worker.

Watch the screen resistor on the pentagrid & 1st IF. Accounts department changed that to 10K from 2 x 22K 1W parallel. If the 10K is 1W it will eventually cook as the screen draw exceeds 10mA. I squared R = smoke.

Marc

Thanks Scraps & Marc

Yeah I've read of doing a change Valve wise...and it might be an option (or maybe a necessity)
7K is what I found from the PDF but Master Yoda I am not with Valve design so thanks for the guide there and the link too.

Shipping always tends to be the killer with the US and now with our dollar taking a nose dive..humm
but still at lest the prices look good compared to here...ups priority from one place was like $50 US for a $20 odd dollar transformer...anyway see if they have the lest secure slower shipping I've gotten a few valves that way.

Yes Marc I reads another post by you ..I probably should have linked it to help save your fingers but you did mention that about the resistors....(bean counters saving a penny probably) still I suppose worth mentioning again.

Transformer.... It seems quite possible they were used across a few brands and models as it probably was an off the shelf part at the right price at the time.

Hope all goes smoothly Marc with your hospital visit ...take care mate.

Thanks guys

PS I know they are probably as common as chips but well I think worth saving from the scrap heap even if it isn't a perfect specimen of that model.

In a lot of cases in that era bits were made all over the place. Many tuners were Stromberg-Carlson. EMMCO (Email) made a lot of stuff for what they built, as well as for others.

A few made bucket loads of resistors & caps and, MSP, Rola etc. Built speaker assemblies with transformer to suit whatever the biggies ordered.

So what you have ended up with is an assembled bucket load of everybody's bits, assembled by a specific lot.

The electrical parts of fifties cars were also a lot like that.

Most of the valve manuals (Franks electron tube pages) will show the recommended impedance for the valve at certain voltages of B+

6M5 was used by many (one will quote) and its pentode appears in other valves.

Marc

Thanks Marc
yeah I thought it would be pretty much that with manufacture of the Day

actually it got me wondering if the tuning gangs and coils etc were done as modular part then supplied to Kriesler etc or done a separate item line of manufacture there..they seem to be a modular set up
help in place by 3 bolts

Arh yes B+ good point...like I said learning curve here... and 6M5 Ive yet to look at ditto the 6X4 seem somewhere some how a large cap was fitted thought I think after the resistor..yet to check that..

thanks for the info
but first things first a transformer is needed...

According to Radiotron Manual 7K Primary for that 250V Thats a common one 5Watt should do.

Hammond 125BSE is one universal type. Digikey cheapest so far There may be others & someone may have one 2nd hand. Antique Radio Supply were selling bobbins for them.

Do not fit E caps above specs. You can go bigger, but that will strip the cathode of the rectifier.

Marc

QUOTE: it might be just me but I find the sound from a 6BQ5 is much harsher than a 6M5 but quite acceptable.

That's a surprise, as 6BQ5s are a popular hi-fi output tube. If you have plenty of gain in your audio amp, try it without a cathode bypass cap.

It might be providing clarity I'm unaccustomed to in the old radios I've only ever used 6BQ5's as a substitute for 6M5's. Definitely a different sounding valve though.

The 6M5's that give the most trouble are the earlier Innoval types. Innoval valves are distinguished by their flat bases. Innoval valves were made from about 1949 to the late 1950's. Afterwards the Australian Innoval series were made as normal Noval valves.

Marcc in the past has mentioned the video output valve 6CK6 as a replacement for a 6M5. I have tried this myself and had satisfactory results.

Here is an extract from the 1950 Australian Philips Miniwatt Innoval book for the 6M5.

Philips 6M5 valve data.

If there is any interest here for the entire (34 pages) book, I can make it available in a pdf file.

If there is any interest here for the entire (34 pages) book, I can make it available in a pdf file.

Actually, a resources (files) area would be a good idea for this site. Maybe with member only access.

There is a documents folder here though currently it only holds the files that are linked to from comments, as per MonochromeTV's post.

If it were to be expanded then, yes, good idea to make it a member-only area.

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A valve a day keeps the transistor away...

Do note and be warned:

The 6CK6 whilst having some similar characteristics (I need to look at data sheets not book) seem at face value, to be the same Pentode structure; the 6M5 has its suppressor grid tied to cathode internally: 6CK6 DOES NOT. Socket Pin 6 must be cleared, if used and only tied to cathode.

Marc

G'day All

Sorry for not getting back to you in the threads

Thank you for all the information and help

Been an interesting Discussion on the Valves there along with the tidbits of "let the buyer beware" always an important things to know when contemplating possible mods for whatever reason, sometimes I think for very good reasons...as in you can improve a situation that a manufacturer was just too cheap to do properly..or the tech just wasn't up to par at the time

Well I was and still am hoping to get my hands on a output transformer, I am just hoping that a guardian angle gets back to me with one

Else weighing up costs of shipping and thanks Marcc I'll grab one from evatco ...better do it quick I suppose with our falling dollar

I did get some spare Valves while I was at it thought ...again more so in regard the 6X4 & possible abuse over time from a larger then spec Filter Cap

So this ones on the back burner....but time for another thread cause I have another!

Thank again guys for a ll the input & help much appreciated

Cheers

Well I finally have an Output Transformer to use for this one now, its not a perfect replacement physically but assured it should work

Taking Note of a comment by Marc else where, I'll have to make sure I get it "phased" right due to the feedback from the speaker side (secondary) of the transformer in the circuit.(if I got that right from memory Marc)

Post back when all is done or if I have any Questions thanks again All

EDIT -------------
Done it Works

The 6X4 rectifier valve was cactus thought (didn't look to healthy to start with..), not sure on the 6M5 just replaced it, thought it at lest doesn't look abused... (I'll check and test it when I can just out of curiosity)

more to do but at a functional stage...

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