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Unread 10-31-2013, 02:15 PM   #1 (permalink)
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Oops eBay. Imminent NOAD...



Just won this on ebay! Not tested, rectifier valve missing, generally "unknown". It was cheap. It's a Linear Diatonic. Early '60s, 15 watts. That's all I know about it except....

My first ever amp was its cousin, a Northcourt 30 (2xEL34 power, 1xECC83 PI, 2xEF86 preamp) also known as the Linear Conchord. I remember it as being loud, almost impossibly clean toned and very, very heavy. I used to run it through an old Vox 4x12 and used pedals for dirt (an old Ibanez overdrive mainly) - it had really nice tone, but once I had a job and some money I bought a marshall and more or less gave it away. The diatonic seems to be a 15-18W version of the same thing with EL84 power instead.

I don't know what I'm going to do with it yet. More details next week when it gets here!

edit - I just looked at the pic, it's a valve short so either the missing one is the pi valve (I don't think so given where it is...) or this is more likely a single ended parallel arrangement OR those power section valves are ECL82 triode/pentodes and the PI is in there (watkins westminster style)
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Last edited by Ozzy Mandeus; 10-31-2013 at 03:13 PM.
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Unread 10-31-2013, 02:18 PM   #2 (permalink)
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Re: Oops eBay. Imminent NOAD...

Very cool find! Def post some clips and gut shots when she arrives!
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Unread 10-31-2013, 02:20 PM   #3 (permalink)
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Re: Oops eBay. Imminent NOAD...

Ozzy,
You, sir, are a certifiable maniac! That's some serious looking iron for such a small unit. Good luck and let us know your thoughts when you get it.
TIA,
Gene
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Unread 10-31-2013, 02:21 PM   #4 (permalink)
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Re: Oops eBay. Imminent NOAD...

I love the knobs. Looks like he raided all the thermostats in his house.
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Unread 10-31-2013, 02:27 PM   #5 (permalink)
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Re: Oops eBay. Imminent NOAD...



Back view shows at least one EL84.... and what looks like a blackburn issue ECC82 at the front (PI maybe? other might be EF86 for high sensitivity preamp) also heater and HT outputs (GR8 for modern safety standards!) so it can power external preamp circuits.... Hmmmmmmm
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Unread 10-31-2013, 02:32 PM   #6 (permalink)
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Re: Oops eBay. Imminent NOAD...

Found a schematic! I googled the name and got no results but some linear thinking later....

Northcourt 15 Schematic Diagram

ECC83 preamp, ECC83/82 PI, 2x EL84 power and an EZ81 for rectifier. I bet I have one of those somewhere....
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Unread 11-04-2013, 12:49 PM   #7 (permalink)
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Re: Oops eBay. Imminent NOAD...

Yay! It's here.... I bet you are all dying to see what it looks like inside....



Mmm, carbon comp and mustard. Nice and neat too. Only odd thing I see so far is the big reservoir cap has had tape wrapped around it to prevent it making a chassis ground. The only other chassis to circuit grounding point is on the input jacks.

Also, I found an EZ81, and the two preamp valves are ECC83 and ECC82, both blackburn mullards, the ecc82 dates as May 1963 and the '83 is from the third week of June 1966. Google tells me this is the week Peter Green joined the Bluesbreakers .



If that ECC83 tests strong, it's easily worth more than I just paid for the amp. It "might" find a home in the V1 position of my bluesbreaker....

Anyway, I'm not doing anything other than look at it and go YES! this evening, I'm banned from amp repairs after dark due to previous circuit breaker tripping incidents.
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Unread 11-04-2013, 01:32 PM   #8 (permalink)
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Re: Oops eBay. Imminent NOAD...

I just used my homebrew single end amp (ecc83/EL84) to test the valves - both preamp valves work fine, but the two supplied EL84s appear to be dud - one works but produces a wierd wind like noise through the speaker, and the other one lit up bright blue then went out and does nothing. If I'm really lucky, then that's what was wrong with the amp....

Pair of EL84s on the shopping list then. I can always "borrow" some from the WEM to test out the rest of it.
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Unread 11-04-2013, 01:39 PM   #9 (permalink)
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Re: Oops eBay. Imminent NOAD...

Hey wait a second...... I'm a dumbass.

One of these EL84s isn't any such thing. The one that does nothing is in fact an EZ81 rectifier valve with all the print rubbed off. Far left valve in the picture on the OP. That's why it's got such odd looking plates : ops: and why it doesn't amplify.

I wonder if it still rectifies given what I just did to it....
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Unread 11-04-2013, 01:51 PM   #10 (permalink)
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Re: Oops eBay. Imminent NOAD...

Very cool, Ozzy! I'm impressed with the design and how well it's laid out. I don't remember seeing anything of that vintage that was as nicely assembled.


Yah, I haven't had much luck either using EL84s as rectifiers!
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Unread 11-04-2013, 03:01 PM   #11 (permalink)
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Re: Oops eBay. Imminent NOAD...

Yeah, it is neat, isn't it!

Maybe if I use a pair of rectifiers and put the EL84 in the rectifier hole.....
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Unread 11-06-2013, 08:49 AM   #12 (permalink)
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Re: Oops eBay. Imminent NOAD...

Progress update...

It checked out for mains safety, so I put a plug on it, connected a speaker and fitted a set of known good valves. It works!

Well, sort of works... it sounds dull, low notes are flabby and when you crank up the volume it breaks up in a fairly awful sounding overloaded Hi-fi sort of way. The low gain input is more or less useless for guitar, it's just too quiet to be any real use.

I'm going to start by checking all the resistors for drift, changing the resevoir caps and altering the input network to the standard guitar type (33k grid stopper, 1M grid leak) with one input jack only. At the moment both volumes act before the first stage, I'm probably going to put the volume after V1a, maybe use the other volume after V1b as a master.
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