EL509 OTL Amplifier

What people are working on at the moment
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andrew Ivimey
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#31

Post by andrew Ivimey »

Sometimes I think I am getting better at wiring up. There is an art to this. But really I just shove things in, realise my mistake, burn fingers, try again and get it right-ish eventually. I will never win prozes for neatness.

I tried that funny aluminium plate stuff and found that unless I seriously bradawed where I was to drill, those lumpy bumps cause the drill buit to fly off.

Oh and don't talk to me about vero board - what was okay back in the transistor age now just ... weell... gggrrrr!

keep up the good work, Steve
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#32

Post by Cressy Snr »

andrew Ivimey wrote: Oh and don't talk to me about vero board - what was okay back in the transistor age now just ... weell... gggrrrr!

keep up the good work, Steve
Yes I am thinking the same thing. I don't like the VeroBoard at all. So much so that it is coming out and a proper bit of tagboard is going in in place of it.
I don't really trust it at valve voltages.

Steve
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Greg
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#33

Post by Greg »

Hi Steve,

if you like the mounting convenience of veroboard but reject it for other reasons, have you thought about using matrix board. Same as vero but no conducting strips. Yo use the lead outs from the components to form a hard wired construction. I've done this with my Pre II and other small projects. Works a treat.

Best wishes,

Greg
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#34

Post by Cressy Snr »

Thanks Greg
Sounds like that could be useful. :)
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ed
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#35

Post by ed »

something like this?
I've always had fun with matrix board, although I dont know what its like with high voltages....
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#36

Post by Cressy Snr »

Hi Guys.

Image

Here's the completed preamp/phase splitter/driver stage module.
I just managed (with a lot of thought) to fit everything within the confines of the aluminium plate. It has been checked out with the meter as far as it can be without connecting the power supply to it. Fault tracing should be reasonably easy though due to the logical layout. The black/blue twisted pair is the heater supply and the two yellow wires couple the feedback circuit to the output rails on the power stage board.

I got rid of the veroboard and replaced it with some tagstrip a bit more man enough for the job. That matrix board should be nice for a furure phono stage.


Pic below is a close up of the interstage coupling caps. These couple the cathode follower outputs from the driver stage to the grids of the power valves. One cap couples to the negative power tube bank and the other to the positive bank. The three zener diodes are part of the circuit that counteracts the degeneration of the upper power tube bank, ensuring a balanced push-pull output from the totem pole power stage. The caps also isolate the negative bias supply to the power tubes from all the previous stages.

Image


Just the power supplies to be built now. Should be a piece of cake compared to this.

Steve
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#37

Post by simon »

OMG! Steve, you have my utmost respect. Don't think I'm ready for an OTL yet :oops:
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Paul Barker
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#38

Post by Paul Barker »

've You got too much time on your hands. There, told you it gets ahead of itself. You have to be real careful with the mouse things come and go in a flash.It's real weard having a computer without a time lag.
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andrew Ivimey
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#39

Post by andrew Ivimey »

Wow! does it work!?
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#40

Post by Cressy Snr »

andrew Ivimey wrote:Wow! does it work!?
It's been checked out on a static test with a multimeter and everything seems to be wired to the right places. I haven't built the power supply yet but as soon as it is done and commissioned then the driver stage will be tested with the HT applied and commissioned before the power stage is similarly tested. Both modules will then be connected together and further testing will take place before it is formally introduced to the speakers.

I'm taking no chances with this bugger.

Steve
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#41

Post by Cressy Snr »

Before I can get the PSU sorted, the chassis needs doing.
This is what I have been concentrating on over the past week.

The look of the casework has been heavily influenced by 1950s radiogram consoles.

Image

The two ivory knobs are from my Mother-in-Law's old 1956 Ferguson radiogram. Transformer cover is an old PreII lid, sprayed burgundy and sandwiched between the two halves of a hardwood chopping board

Valve holes were cut with hole saws and the edges rounded over with a router. The slots will provide ventilation for the rectifier heatsink.

I'll have the PSU underway this week.

Steve
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colin.hepburn
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#42

Post by colin.hepburn »

Hi Steve
Thats looking good those knobs do give it a fifties radiogram look just needs a magic eye and your of a running :P
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Nick
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#43

Post by Nick »

Now look Steve, just when I am trying to be neat with the 6c33c amp, you go and up the stakes again. Bummer.

Looks very, very nice, how about a couple of jacobs ladders at the back to add that extra touch :-).

I think you should call it the Hilversum 509 :-)
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#44

Post by steve s »

colin.hepburn wrote:Hi Steve
Thats looking good those knobs do give it a fifties radiogram look just needs a magic eye and your of a running :P

don't confuse the man colin.. it will all have to come apart and be redesigned to fit a magic eye in the right place..

i hope it sounds as good as it looks..

good job steve

steve
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#45

Post by Cressy Snr »

Nick wrote:
how about a couple of jacobs ladders at the back to add that extra touch :-).
I don't think the missus would appreciate blackened curtains and the ozone would get a bit strong :shock: :D

Steve
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