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  #11  
Old 5th April 2013, 08:53 AM
John Caswell John Caswell is offline
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Default Re: 50 Watt amplifier

Hi all,
I know you can make them but "Tube Town" in Germany (tube-town.net) supply the Octal to B9A converter plates I mentioned above, plus a good range of JJ, Mundorf and F&T capacitors with 500V dc ratings.
I think I will have a chat to a "tin basher" friend of mine about these plates.

John
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  #12  
Old 5th April 2013, 12:41 PM
Matthew Snell Matthew Snell is offline
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Default Re: 50 Watt amplifier

"but frankly for a design first shown in Wireless World April 1957 I am seriously impressed."

Me too!

I thought the amp had some hum at first - turned out to be too many interconnects draped across the sofa. Shorted inputs gave absolutely nothing audible with my ears glued 2" away from the speakers at full volume!

Initial listening: impressed with phenomenal detail (too much on some recordings - Tallis Scholars "Live in Oxford" was almost uncomfortable to listen to) but suspect this might be down to the unlimited bandwidth. Which could be tweaked. With other recordings the high detail is lovely and very rewarding. Loads of "room", very fast and pacy. I like it! If KT88 is a bit of a Daimler, this is more of an Aston Martin. Very classy indeed.

I will be doing some back-of-the-envelope costings in the next few days - thinking in terms of 6D22S rectification and monoblocks. Also thinking of slightly more basic finish than the current models - I happen to like the chrome transformer caps of the current range, but they don't half force the asking price up! Upright, surface mounted transformers and pierced metal cover anyone?

I'll report further when I've a better idea how viable this project might be.

Lovely project John, and thank you.

Matthew
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  #13  
Old 5th April 2013, 05:09 PM
John Caswell John Caswell is offline
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Default Re: 50 Watt amplifier

Hi all,
Piccy's of the 88-50 courtesy of Matthew, I hope

John
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File Type: jpg 88504.jpg (130.8 KB, 54 views)
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  #14  
Old 5th April 2013, 05:10 PM
John Caswell John Caswell is offline
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Default Re: 50 Watt amplifier

And two more, I hope.
As you can see they are not identical physically but were made on a pair of u/s back to front WD88 chassis. Previous posting gives you a basic idea of layout whereas this one internal wiring. Tag boards could possibly be condensed, but then no room for boutique components. The KT120 bias Rs and Cs will the hard wired in onto the chassis and the g2 stopper Rs as close to valve bases as possible as are the g1 stoppers which are carbon composition Rs, Decoupling Cs are some I have handy and will be used in the final beasties. Kit versions will be electrolytic to keep costs down
Power Txs are multi tapped primaries for use anywhere in the World. Kit versions are likely to be the same but obviously engineered to suit the amp better. Series Rs used in the anodes of the rectifiers to limit HT and hot switching (especially with the GZ37 and EY84) and will still be there in Kit version I guess. As I said not sure of final layout, I am playing with it at the moment, also not sure whether to supply kit chassis with Octal cutouts for the two small signal valves and supply reduction plates for B9A type valves. Comments useful here please.
More anon

John
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File Type: jpg 88502.jpg (114.3 KB, 57 views)

Last edited by John Caswell; 5th April 2013 at 05:24 PM.
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  #15  
Old 5th April 2013, 09:35 PM
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Greg. Greg. is offline
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Default Re: 50 Watt amplifier

Quote:
Originally Posted by Matthew Snell View Post
Also thinking of slightly more basic finish than the current models - I happen to like the chrome transformer caps of the current range, but they don't half force the asking price up! Upright, surface mounted transformers and pierced metal cover anyone?
Hmmm, to attract the kit builder who cares about aesthetics, I don't agree. To be sure, drop through Tx's are far better looking than the surface mount option. Surface mount also require two end caps instead of the drop through one, and your suggestion of a pierced metal cover IMO is not the way to go.

I don't know who now makes your Tx's but through personally dealing with SP Wound, they supply basic end covers with their Tx's that are either finished in black paint or dull metal plating. You could offer this type with the kit, but suggest if the customer wants chrome plating of the end caps, they'll need to arrange for themselves, which is what I did on receipt of my Tx set from SP Wound for my WAD 300B PP Clone.
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  #16  
Old 5th April 2013, 11:05 PM
John Caswell John Caswell is offline
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Default Re: 50 Watt amplifier

Drop through txs are a big waste of space and engineering wise not a very good way of going as they put all the tx cores in the same plane, so aiding magnetic field mutual coupling and will also transfer more noise and energy to the chassis, which goes against all I have been taught and have taught over the past many years.
To me chrome covers are just a poncy waste of money and I don't think they look very pretty either, also two plain end caps are a damn sight cheaper that chrome ones.
In commercial stuff a lot of money that could be spent on the electronics is spent on making something look pretty, not for me I am afraid.
I really don't care too much about the basic looks as I regard the amp as something to be used but not seen, very much like a car engine.

John

Last edited by John Caswell; 5th April 2013 at 11:07 PM. Reason: Additions
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  #17  
Old 5th April 2013, 11:42 PM
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Default Re: 50 Watt amplifier

I don't doubt everything you have said, but what you like is not what most people want. Matthew will need to work this one through.
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  #18  
Old 6th April 2013, 12:27 AM
John Caswell John Caswell is offline
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Default Re: 50 Watt amplifier

Its good being the odd one out, don't run with the herd.
As a Spanish wit once said "If they give you lined paper, write the other way!"

John
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  #19  
Old 6th April 2013, 09:20 AM
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pre65 pre65 is offline
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Default Re: 50 Watt amplifier

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Originally Posted by John Caswell View Post
Its good being the odd one out, don't run with the herd.


John
My sentiments exactly. Like my 833a monsters.

The aesthetic impact of an amplifier is quite personal, to me the "Greg" approach is a bit "showy", but that is (as Greg says) what a lot of people go for.

I quite like the basic "utilitarian" look like on the Quad 11 amps.
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  #20  
Old 6th April 2013, 10:45 AM
Chris Chris is offline
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Default Re: 50 Watt amplifier

If it was me I would try to market every stage, so one could select just to buy the instruction/parts, plans etc. Instead of holding large stock of Tx's it would be better to purchase on here and have them sent directly from the supplier, some may prefer to have everything supplied in one package, others prefer to source their own capacitors and wires etc.. Just an idea I may be completely wrong..
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