JCM800 4211 restoration

Indie · Post by **Indie** » Sat Oct 30, 2010 12:04 am

Hallo friends

I am currently working on two amps restoring......first is 1969. Bassman....second is JCM800 model 4211...

I am here to ask for few very important informations for my projects...

Let me describe what I am realy doing:

JCM800 was changed to solid state power amp section by somebody...

So that ''smart'' guy pulled out output tubes and output tranny ...an add solid state circuit under the chasis....

Now I am waiting ...ordered parts to come from Germany....

But!!!

Power tranny is changed cause he had to rewind one secondary to give the power to his transistor circuit....
So he unwound 98v secondary....and wound new 60v one....

Hi voltage secondary stayed unchanged but it gives 325v.....have two green ....without center tap....is it ok?

So I hav to rewind 98v again ...but I have a problem cause I have no winding plan for this transformer...and I don't know what diameter of wire I have to use....to reach properly current rating.....of 50 mA

If someone can halp me with this secondary ...or if somebody have information how many turns I have to make..and what diameter of wire..??
I counted while I was unwinding 60v secondary that it has 96 turns so ...I calculated that I need 1,6 turns per volt...is it correct?

My transformer have red stamp ..and it says: DET-4145F
I think it could be Drake tranny

I have no money to buy new one now ...so I would like to rewind this secondary...and make it to run again...specially cause primarys and hi voltage secondaru survived in original shape.....

6,3v secondary for heaters is not problem cause it has only 11 turns of wire...but if someone knows what diameter could be good for 7A curent I will be very thankfull

Sorry about my bad english

All the best Alex

Indie · Post by **Indie** » Sat Oct 30, 2010 12:16 am

Cliff Schecht · Post by **Cliff Schecht** » Sat Oct 30, 2010 2:34 am

Holy shit! I hope you never fired that up as is.. I'd recover what wasn't modified and replace the test. It looks like the guy was a real hack and I wouldn't trust anything he touched.. Luckily the insides are relatively unpacked so your job is just undoing the damage and replacing what has been modded. The HV flying around all willy nilly is scary.

Indie · Post by **Indie** » Sat Oct 30, 2010 10:03 am

Of course ...I am working on completly restauration......backing up amp in original shape...

This is the reason why I have to rewind 98v secondary....cause it is missing ....it is prebias secondary ...

So if someone can halp about this...

I alredu bought OT tranny few missing resistors and one electrolytic can...el34 tubes and their sockets too

Indie · Post by **Indie** » Sat Oct 30, 2010 9:10 pm

So I have a friend who can rewind 98v secondary for me......

Does anyone knows what string diameter is good for 98v prebias secondary winding if we know that current has to be 50mA???

Cliff Schecht · Post by **Cliff Schecht** » Sat Oct 30, 2010 11:06 pm

I guess you misunderstood what I meant. Specifically I hinting at the fact that the guy mucked with the transformer so I wouldn't be so trustworthy of it, unless you can verify that the other windings are as they should be. It may be alright as is too, I just don't trust hacky work like what you've posted.

You could try contacting the original manufacturer and see if they'll share the spec you're looking for, some transformer companies are generous with their info while others like to safeguard their "secrets". If they won't provide the information, any winder worth his salt should be able to figure out what gauge you need to do the winding.

Indie · Post by **Indie** » Sat Oct 30, 2010 11:34 pm

ty for advice....

I have done detail inspecting...and I am shure that all primary windings are original.......just as 330v secondary is orignal too....

I recognize that....cause here I can see original paper between windings fixed with some kind of shellack.....and simply I can see that there were no interventions...

The guy just unwound 98v secondary....cause he didn't need it....cause he pulled out ...power tubes...and he simply didn't need bias 98v winding....
Instead of that he wound 60v with fat wire for his transistor powered circuit added under chasis....

so I already removed that 60v winding and calculeted that I have to wind 1,6 turns per volt.....

Everything other is ok and works well except winding that is mising...

I tried with manufacturer but there was no answer...

One tech helped me ..told me that 0,4 mm wire will be ok ...and that is good to put a bit stronger diameter.....than usually goes.....to prevent tranny overheating....

6,3 volts HT secondary is the only one that need to be wound with fat 1,7mm wire...cause it need to give heater power to 9 tubes....
this is the reason why that smallest secondary have 7A...

so wish me luck with reparing secondary that is mising.....hope it will work fine......

edit:
of course I will not do this alone......I will go to the friend who have winding machine and lot of expirience..

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JCM800 4211 restoration

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