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Old 29th Jun 2022, 12:36 pm   #1
snowman_al
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Default HH Scott LK48 restoration

Some of you may have seen this on Pinkfish already.

I always fancied an American Scott amplifier.
The HH Scott LK48 is the kit version of the Scott 222D. Circuit here: http://hhscott.com/pdf/fs/LK48B_C1.JPG

This one came in very good condition physically with the correct knobs and decent case etc.. Who ever constructed it originally did an excellent job to.
But one output transformer was open primary... Off to Ed for a rewind.

I read all the US sites with 'do this', 'change that' etc. most of it unnecessary in this case. I've replaced most of the coupling caps, but the originals were fine in value and leakage. I very carefully monitored the electrolytics for days, all good. A few resistors had drifted high so the got replaced and the bias rectifier (selenium) was poorly so that got repacked with 4 silicon diodes.

The valves were all original apart from a couple of odd ECF82s replaced with US 6U8s, but the four 7189 outputs needed replacement to set and balance the bias properly.

And it is huge and weighs 17 kilo grams!

Alan

Album here; https://ibb.co/album/vZdP16
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Old 2nd Jul 2022, 7:40 am   #2
vinrads
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Default Re: HH Scott LK48 restoration

Very well done Alan ,nice amp it reminds me of the Juke box amps I repair/restore ,Mick.
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Old 20th Jul 2022, 9:25 pm   #3
qualityten
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Default Re: HH Scott LK48 restoration

I've just noticed this restoration. Thank you for the detailed pictures of your work, and the beautifully crisp circuit diagram.

I have the 222C, with the addition of the 222D bias arrangement. I keep wondering whether to try and locate a suitable 240V power transformer for mine. I presume you kept the 117V one?
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Old 21st Jul 2022, 8:52 am   #4
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Default Re: HH Scott LK48 restoration

Hello,

Nice job Alan.

Iíve a Scott Kit LK-72 (B) with a UK spec 230V mains transformer. This was a UK spec kit and was assembled by someone living in Surrey in the UK in the early 60ís. It been quite nicely made.

This is the bigger 35 watt/channel job using 7591 valves. The transformers are quite meaty with a generous amount of Iron. I got this at the audio jumble quite a few years ago, however, sadly the front panel is graunched in one corner and has one wrong knob along with no cabinet, otherwise it's in good shape.

Terry
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Old 21st Jul 2022, 9:42 am   #5
snowman_al
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Default Re: HH Scott LK48 restoration

Quote:
Originally Posted by qualityten View Post
...
I have the 222C, with the addition of the 222D bias arrangement. I keep wondering whether to try and locate a suitable 240V power transformer for mine. I presume you kept the 117V one?
Yes it is a 117 volt version. I've a 1000VA step down transformer and it runs at 117 to 120 volts (depending on mains voltage).
The Scott transformer runs cool even after a few hours of use. Much cooler than a Leak Stereo 20 transformer.
I'm not sure a 240 volt Scott transformer will pop up any time in the future...
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Old 21st Jul 2022, 12:19 pm   #6
Ted Kendall
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Default Re: HH Scott LK48 restoration

Quote:
Originally Posted by snowman_al View Post
I'm not sure a 240 volt Scott transformer will pop up any time in the future...
Ed to the rescue?
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Old 21st Jul 2022, 9:33 pm   #7
qualityten
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Default Re: HH Scott LK48 restoration

Apart from the inconvenience of having to use an additional transformer, I have sometimes vaguely (ignorantly) wondered if our double mains frequency affects the performance of a US-made power transformer in any way.

But, that question is better asked in the Components and Circuits forum, so I do not expect a reply here. FWIW, I have successfully replaced the US mains transformer in an Eico ST40 with one from a Hammond organ, as both used 7591 valves.
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Old 24th Jul 2022, 8:10 am   #8
Ted Kendall
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Default Re: HH Scott LK48 restoration

The rule of thumb is that the mass of the transformer core varies in inverse proportion to the supply frequency, all other things being equal. So the optimum mass for a 50Hz transformer is 20% greater than that for an equivalent 60Hz design. In practice, a 60 Hz design is usually satisfactory at 50 Hz unless designed to the bone, but will run hotter and more noisily at the lower frequency.
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Old 25th Jul 2022, 9:06 am   #9
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Default Re: HH Scott LK48 restoration

That's really helpful Ted! A rule of thumb that I can understand and use in future.
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Old 25th Jul 2022, 11:50 am   #10
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Default Re: HH Scott LK48 restoration

Just arrived for refurbishing. Needs transformers and the rest.
A bit of a state!
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Old 25th Jul 2022, 12:02 pm   #11
qualityten
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Default Re: HH Scott LK48 restoration

Wow Jon, that does need a lot. What model is it? Could you post a new thread showing your progress with the refurb?
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Old 25th Jul 2022, 1:12 pm   #12
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Default Re: HH Scott LK48 restoration

I have to estimate the refurb first and get the client to agree before starting the job.
Yes, I wasn't expecting so much missing.
No transformers, new to be made, capacitors broken off so I will make new paxoline holders.
The client told me it was a Scott 299, it isn't. It is an LK48.
Has the wrong valves for the 299. 7189s not 7591a's, a blessing in disguise really as 7591As are best part of a Kings ransome to buy. 7189s are 6P14P-EV and a reasonable price.
Not looking likely though as there is an immaculate LK48 on fleabay in the USA for £600 plus postage. I think that will be cheaper than repairing this one.
If I get the go ahead, I will start a post on the progress.
We'll see.
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Old 25th Jul 2022, 1:48 pm   #13
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Default Re: HH Scott LK48 restoration

The first two 299 models, 299A and 299B did use 7189 valves. The Scott schematic database is very useful. http://hhscott.com/database/vhhs_00011.html
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Old 25th Jul 2022, 3:28 pm   #14
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Default Re: HH Scott LK48 restoration

I believe your client is correct (and as qualityten) it is a Scott 299a or 299b.
The mains transformer bracket is a give away then check if it has 3 neon indicators on the front panel. The 222 / LK48 are different in both these respects.

Not sure there is enough to actually build a 'proper' Scott there unfortunately?

Scott 299 Audiokarma thread here. https://audiokarma.org/forums/index....-story.715312/
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Old 25th Jul 2022, 3:32 pm   #15
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Default Re: HH Scott LK48 restoration

Hi,

If Iím not mistaken the Scott 299C was the factory made version of the LK-72, which was the kit version - I think

Attached a couple of pictures of the LK-72 I have lying around the workshop.

Terry
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Old 25th Jul 2022, 3:47 pm   #16
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Default Re: HH Scott LK48 restoration

Unfortunately, I have no front panel and no model number on the chassis. Just guessing really.
There is a 299 with 7189s going for £650 on eBay.
I reckon more than £1300 by the time I have a working model and I don't know if the case and front panel are in good condition either, I have not seen them.
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Old 25th Jul 2022, 5:20 pm   #17
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Default Re: HH Scott LK48 restoration

It might be possible to source two output transformers from the US, but they would not be cheap. These amplifiers wouldíve been luxury items in the UK in the early 1960s.
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Old 26th Jul 2022, 6:11 am   #18
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Default Re: HH Scott LK48 restoration

Yes, output transformers can be sourced from the US the mains transformer can be found from Hammond in Canada.

I think it will be a non starter though. Many components have been cut and misplaced.
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