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Old 28th Feb 2008, 10:55 pm   #1
Steve_P
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Default (Let’s have some music) MAESTRO 756

Well most of you know I like the Eastern European Sets - and I thought this was one when I bought it on Ebay. But when it came, I had a bit of a shock. This set - Maestro 756 - was Turkish! Interesting to note that the BBC stations were not on the dial.

Well, the cabinet was all wood, and quite nicely made. Inside, however, it was a tidy looking rat’s nest. Metal Rectifier, then the valves were ECC85, ECH81, EF89, EABC80 and EL95. The output stage was small.

It looked OK inside and out, so after changing the Control Grid capacitor, I switched on to see what it would do. This set was set up for the highest voltage it could be - 220v and here in Sunny Bolton, it’s usually 239 Volts. Oh well, it’s been used on that already, so let’s see what happens.

Long Wave and Medium Wave were quite lively, Short Wave was Dead and FM was equally uninspiring. Put the set on the outdoor antenna and it livened up a lot on all three AM Bands, still nothing on FM.

10.7 Mhz got through, but nothing else. A new ECC85 brought FM in, everything was about in the right place, but FM sounded weak still. The caps on the Discriminator were changed - no joy. In fact, the whole set seemed a bit poor. A spare EABC80 improved things a lot. Two valves changed. I dropped the mains to 220v and it stayed the same, so we were almost home.

A dial lamp was fitted, and a look at the valves showed that this set’s problems were down to 2 problems. Odd Manufacturer of Valves which had all been overrun.

So, I needed to modify the set for 240v operation. Mains back up and measure across the valve heaters. At 240v, the valve heaters were 6.87 Volts. So, we needed to drop about 0.5v.

So, current would be 0.435 + 03 + 0.2 + 0.45 + 0.2 = 1.585 Amps.

Using Ohms Law, R = 0.5 / 1.585 = 0.3 Ohms.

The power it would dissipate is about 1.585 x 0.5 = 0.79 Watts.

Time to look in my magic box. 3 off 1 Watt 1 Ohm Resistors. That’ll give us 0.33 Ohms and plenty power.

The HT was still within tolerance for the valves, so I fitted these three resistors above the chassis, where the heat would be easier to dissipate and then tried the set. Sounded OK so I called it a day.

I always do these little calculations when doing a job like this one. Best to know what you’re looking for before you dive into the …er….junk box!

Nice looking set in the end.
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Old 29th Feb 2008, 2:58 am   #2
Robert Darwent
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Default Re: (Let’s have some music) MAESTRO 756

Hello Steve,

That's a lovely looking set, reminds me a lot of the Bush VHF62, you've done a first class job of restoring too. Very well done!

Your thorough description of lowering the mains supply is also excellent and a very useful reference for anyone wishing to carry out this modification on other sets that were intended for less than a 240v supply.

First Class!
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Old 29th Feb 2008, 11:07 am   #3
Radio_Dave
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Default Re: (Let’s have some music) MAESTRO 756

Well done Steve,

That's a very nice radio

Regards
David
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Old 1st Mar 2008, 9:29 am   #4
Mike Phelan
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Default Re: (Let’s have some music) MAESTRO 756

Nice job, Steve - has a certain Grundigness about it!
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Old 1st Mar 2008, 1:37 pm   #5
geofy
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Post Re: (Let’s have some music) MAESTRO 756

Well done Steve, and the very name Bolton conjures up images of 'proper' engineering. Maybe a certain much missed steeplejack had something to do with it !

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Old 4th Mar 2008, 9:07 am   #6
howard
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Default Re: (Let’s have some music) MAESTRO 756

Well done Steve ,

What a nice radio and I suspect the first Turkish built vintage radio on the forum.

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