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Old 14th February 2006, 02:45 PM   #1
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Default Schematics needed for Heathkit S33

Hi,
As the title really, Does anyone have the schematics for a heathkit S33, after listening to this amp for a few months i have decided its finally time to do a full rebuild and make a nice new chassis for it, Haveing the schematics would help greatly.
Many Thanks,
OWen
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Old 14th February 2006, 04:50 PM   #2
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Owen,

Did you look here ?

/Hugo
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Old 14th February 2006, 05:12 PM   #3
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I've never heard of the S-33 - maybe was sold under a different number in US? SA-3 is closest I can think of...
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Old 14th February 2006, 06:05 PM   #4
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The S33 is a SE EL84 amp. There is an amp on ebay at the moment that appears to use the same Chassis / Power transformer BUT From what i can see is a Mono EL84 PP amplifier model MA-5 http://cgi.ebay.co.uk/HEATHKIT-MA-5-...QQcmdZViewItem

Not sure if it was called something different in the US or not but i have seen a couple of them turn up on ebay since i bought mine (and typicall as it is they have all gone for less than i paid for mine)

many thanks,
OWen
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Old 15th February 2006, 12:43 AM   #5
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Quote:
The S33 is a SE EL84 amp.
Owen,

That in itself is enough to go on, since you are planning on a new chassis and recycling the "iron".

I'm guessing that the O/P trafos don't have UL taps and that Heath used pentode mode. Choose between 2+ WPC triode wired and approx. 5 WPC pentode wired. Loop NFB is not needed in triode mode. If you go pentode, regulate the screen grid B+ (say a VR150), as linearity is BETTER that way.

A 5965 or E180CC/7062 will provide ENOUGH drive for the EL84 in either triode or pentode mode.
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Old 15th February 2006, 08:10 AM   #6
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at the moment the drivers are some nice mullard ECF80's. I really like this amp so i would like if i can find the schematics of the original aswell, this ofcourse dosnt mean i will go with the original schematics but it would be nice to see how it was done incase i ever do decide to build another one.
The output transformers only have 6 wires on them, 3 going to the amp and 3 going to the speaker posts.
From my research the ECF80 wasnt a very popular tube to use as a driver/ preamp tube, would be interesting to see how thay have done it here.

But yes, any other fairly simple yet decent sounding SE EL84 amps, preferably pentode mode (the little extra power is usefull because of the size of my listening room and my speakers being pretty rubbish (next project mabey))

many thanks,
Owen
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Old 15th February 2006, 09:24 AM   #7
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checked output transformers and one wire (red) goes to B+, another wire (red) goes to pin 7 on the EL84, and the third whire (yellow or white, not really sure) goes to pin 9 on the EL84. I forgot how simple this amp was, i will probably draw the schematic myself, only thing that is even slightly complicated is the driver's and thats only because there is a PCB for them..
Owen
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