Remember These?

[Cressy Snr]

A lot of mechanical work today, caused by me changing the layout because I wasn't happy with it.
99% of the bits have been attached to the board and heaters are live on both the 5687s and the 13E1s:

[Cressy Snr]

CLC power supply for the output stage can be seen to the left of the output valves and uses 2200uF, 200V panasonic caps.
Large JJ, 100 + 100uF cap above the input stages is the final CRC section of the 300V supply, which will be derived from a voltage doubler:


AC for the heaters reads 26.8V per 13E1 and 12.3V for the input/drivers.
That'll do for me.

[Ray P]

Excellent progress Steve.

You put me to shame as I haven't done anything on my projects; head is so full of cold that I've just kept warm and comfortable by the TV. I did enjoy watching the recent 'Spitfire' movie though. Tomorrow!

[Ant]

I've found couple of veroboards if you want them for the audio circuit components?

[Cressy Snr]

I've found couple of veroboards if you want them for the audio circuit components?

That might be an idea.

[Mike H]

Rustic wall!

[Cressy Snr]

Rustic wall!

Aye, it was a bright idea of the missus around thirty years ago. She wanted to go all cottagy.

[Cressy Snr]

Is this untidy enough to qualify as a breadboard?

[Cressy Snr]

Output stage PSU and the Septar valve bases are wired up apart from the cathode CCSs


Off load DC voltage is a healthy 168V...ish.
No music from it this weekend unfortunately.
Input stage voltage doubler power supply is next.

[Ray P]

Good work Steve - slow but sure wins the race!

Given the transformer rating I doubt if the load is going to drag that voltage down much.

Looking forward to next weekend's installment - its like going to Saturday morning flicks, just need to pop into Woolworths for a bar of nougat.

[Ray P]

It all looks pretty neat and tidy too, I can tell you've been thinking about this.

[Nick]

Is this untidy enough to qualify as a breadboard?

Its a start

I can tell you've been thinking about this.

That's the bit that breadboards are meant to avoid

No time to worry, fret and talk yourself out of trying the idea, just see if it works, and if it doesn't nothing is lost.

[Cressy Snr]

Couldn't stop at the one power supply, so now we have two:


Full wave voltage doubler supply is now live and uses high voltage Schottky SiC diodes.

357V off-load, so I'm pleased with that. Should give plenty of swing from the driver stage.

[Cressy Snr]

Change to the cathode resistor value on the driver stage will set its cathode at 8V and 15mA bias, rather than 4V, and will give just about the maximum undistorted swing I can get out of the 5687 as a driver, given the generous level of HT I will have available. Swing is around 230V pk-pk, so plenty of welly from the driver, which ought to in turn, allow a decent level of feedback.

[Cressy Snr]

Did some work on the house this morning, then came to a convenient place to stop. I have to buy more materials tomorrow in order to get the penultimate phase underway.
So....this afternoon I was able to do bit more work on the breadboard, wiring up the cathode constant current sinks, so that I was then able to test the output stages.



The valves came up nice and smooth and settled down to their bias, very close to each other. The two appear to be nicely matched.
The 2.4R resistors turned out to be 2.6R when measured and at these low levels, that's a fair way out, so the current the valves are drawing is 480mA, which is a bit short of the 520mA I had wanted. The valves are dissipating only 71W, nearly 25W short of their theoretical max. This means that with a bit of judicious tweaking of the adjust resistor value, it should be easy enough to push the tubes' dissipation up a bit. 85W would seem therefore to be a reasonable target; which is about as far as I'm prepared to go.