Remember These?

[Mike H]

You could just use a big sheet of metal temporarily? Not pretty but works ...

[Cressy Snr]

You could just use a big sheet of metal temporarily? Not pretty but works ...

Aye, could do that. Might be an idea to build it on a breadboard first anyway.

Did I just say "breadboard"? Quick the sky is falling!

But seriously, building it on a bit of wood first is probably the best policy in this case.
It'd be daft not to, as I've loads of offcuts from the house remodelling project.

[Cressy Snr]

I'm really going to be breadboarding now as the missus has decided we need a new sofa and chairs and it's a ruddy sight more expensive than I thought it was going to be.

Humbug

[Mike H]

Oh dear. Yeah they do that. Missus's. A guy on one of the motorbike forums said recently his SWMBO has decided it's America for their hols next year. That's pretty much scuppered his motorbike acivities calendar for the same period. Costs also being an appreciable factor.

[Cressy Snr]

OK, so in the spirit of breadboarding, or chainsaw hi-fi as RD calls it, the transformers are mounted on the bit of ply and everything has been tested.

The correct AC off-load voltages are appearing where they should and the CL60 inrush current limiting thermistor is doing a fine job of stopping the breaker tripping when the 1200VA's worth of toroids are all fired up at the same time.

Centre is the 1KVA HT transformer for the output stage.
One 115V winding for the output stage, the other will feed a full-wave voltage doubler, to give 300V DC, for the input and drivers.
I'm doing this because I have no suitable transformers that'll give the right HT for the 5687 or ECC99 cascade. Can't see the doubler being a problem for this low-current, input/driver application.
Left is the heater transformer for the 13E1s
Right is the heater transformer for the input and driver stages.

[ed]

good to see the hammer is within easy reach if something misbehaves.....waytogo

[Cressy Snr]

good to see the hammer is within easy reach if something misbehaves.....waytogo

Well you have to take those kinds of precautions with OTLs

[Cressy Snr]

Well we have heaters now:


It's been a while since I last saw these beauties all lit up

27V when powered up, so not far off spec.

The far valve is nowhere near as bright as it looks on the pic. They are both the same, dull red, so not a problem.

[Ray P]

Looking good Steve.

Time for a

[Cressy Snr]

Looking good Steve.

Time for a

Definitely!
Just cooking the second pair of valves:

These are the oldest pair; from the late 1950s, I think. They don't have the extra cooling fins on their anodes, so I will be using the newer ones in the OTL. Given that they'll be running nearly 80W dissipation each, I don't want to thrash unnecessarily, the older ones.

[Wolfgang]

good to see the hammer is within easy reach if something misbehaves.....waytogo

Well you have to take those kinds of precautions with OTLs

If my little circuit works which I am developing right now you won't need a hammer anymore! Some CMOS logic will disconnect B+ before the tube can damage anything or is damaged.

[Cressy Snr]

If my little circuit works which I am developing right now you won't need a hammer anymore! Some CMOS logic will disconnect B+ before the tube can damage anything or is damaged.

Hmmm. Now that's interesting!

[Cressy Snr]

Well I went into the bags of components to discover I had only ordered enough for one channel!
Going to have to put in another order now for the other channel. What a fooking wally!

[pre65]

Well I went into the bags of components to discover I had only ordered enough for one channel!
Going to have to put in another order now for the other channel. What a fooking wally!

Don't berate yourself Steve, it's part of getting old(er).

[Cressy Snr]

Well I went into the bags of components to discover I had only ordered enough for one channel!
Going to have to put in another order now for the other channel. What a fooking wally!

Don't berate yourself Steve, it's part of getting old(er).

Indeed!