Will this power transformer work in the 18W liteIIb?

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chopin2323
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Will this power transformer work in the 18W liteIIb?

Post by chopin2323 »

I have an old amp from the mid sixties that runs 2 EL84's and 2 12AX7s with a EZ81 rec tube as well. Will the transformers work for an 18W LiteIIb build?
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Daviedawg
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Re: Will this power transformer work in the 18W liteIIb?

Post by Daviedawg »

Welcome to 18 watt. Repurposing an old set up is great.

It sounds like it should result in a working amp. But maybe not working as well as a purposely selected transformer to achieve the target voltages which the 18 watt tone depends on. Also there are no guarantees as modern valves may not operate at optimum level with the same current draw. If you can see any more information especially the current capabilities of the transformer or the make model or even the model of amp we can help more.

Or, assuming they come from a working amp, you could carry on to see what results. If not working then some care is called for to see that it is a safe route to go.

Dd
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zuceno
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Re: Will this power transformer work in the 18W liteIIb?

Post by zuceno »

An "old amp from the 60s"? And it is working?

Perhaps you should say more. Tell us what you know - with pictures, if possible. You might be contemplating doing something to a classic amp that you do not recognise as a classic amp!

I thought about this, and the amps with that line-up that spring to mind are the Marshall 20W PA head, an Elpico, and the Sound City version of the Elpico. The Marshall and the Sound City are very collectable, and would fetch good money on eBay. The Elpico is less collectable, and would make about a quarter of the >/= $1200 that the Sound City would fetch, even though the amps are internally similar.

And a caveat - there are a couple of Italian amps with a similar valve complement which use a strange autotransformer for output. I do not know much about these, except that they need to be set up differently from a standard OT.
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chopin2323
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Re: Will this power transformer work in the 18W liteIIb?

Post by chopin2323 »

Hey, thanks for the replies! The amp is actually a Decca amp made in the Japanese Teisco factory. Pretty sure it isn't worth my h at all. Amp does work but just isn't very pleasing at all unless you hAve it reeeally cranked and breAking up. The transformers don't really say anything but what appears to prob be date code. I will give the exact numbers when I get home from work.
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zuceno
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Re: Will this power transformer work in the 18W liteIIb?

Post by zuceno »

chopin2323 wrote:
Fri 07/05/19 8:03 am
Hey, thanks for the replies! Amp does work but just isn't very pleasing at all unless you hAve it reeeally cranked and breAking up.
As you might expect from a hifi extension amp, then!

You're probably right that this is low value. I've actually got one of its predecessors somewhere, but that Decca has an evil tube to replace (6HU8/ELL80) so I've never done anything with it.

Yes, that does sound like a potential Lite conversion, but you might find the output transformer restricting at the end of the day. OTOH if the amp is "tied down to be clean" by using negative feedback and/or screen taps it might be possible to free up the sound - then you find it puts out more power than the designer intended, and pop goes the speaker!

See what more you can find out about it.
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chopin2323
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Re: Will this power transformer work in the 18W liteIIb?

Post by chopin2323 »

Decca DMI-73
This is the schematic that I got luckily from the back of the chassis. It looks pretty different to me than I am used to looking at. The grid stopper resistors at the input are a little confusing on how they are working. Also the negative NFB.. is that a normal way of doing that? 330k I guess could be reduced a bit. I guess also that the tremelo stage isnt really amplifying the signal but just controlling the trem? Any guidance on how to make it less HiFi sterile and with earlier breakup would be greatly appreciated. Still want to 18W it, but really would love to know how to dig into THIS particular circuit as well to experiment. As far as the trannies, there really isnt anything there but what looks like date codes. I you would like to see that then I will put that down for you too.
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zuceno
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Re: Will this power transformer work in the 18W liteIIb?

Post by zuceno »

Jeepers - my gast is flabbered. My oh my but I have never in my wildest dreams come across a Decca guitar amp - but I have also never seen a hifi amp with a tremolo circuit. And you can tell it is a Teisco? That really is a rarity.

If it has variable voltage input taps, 100V and 120V etc, I would be seriously tempted to put that on eBay with a reserve around $400 in a 7 day auction that starts and finishes around noon GMT on a Sunday. That timing gets Japanese buyers staying up until around 11pm to bid, while early birds can also bid from the US. This could be like the Sound City/Elpico thing I mentioned above, where the Sound City badged amp is more collectable. I can see that, to a Japanese collector, a Decca-badged Teisco would have appeal, whereas an ordinary Teisco would not.

Oh yes, the feedback connection - that is a common way of doing it, and, no, you're not thinking about it the right way. You would use a larger resistor to reduce the feedback, or disconnect the loop to eliminate the feedback. That should get it sounding more like a guitar amp.
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