Remember These?

[Ray P]

I was going to suggest a saucepan too - should be possible to polish it up as natural metal finish, which could look nice. Maybe consider potting the toroid inside too?

[Ray P]

The insides:

Looks like you built it from a Transcendent kit!

[Greg]

That Hotrox wire looks good. Thanks for the link. Looking at your photo on HFS, it appears that your cover is not sitting properly onto your amps top plate. Is it resting on the top of the Tx? I was very careful that my diy cover made no contact with the Tx in any way. Even then, I ran an earth wire from it just to be certain. My KaT88 is still working well in this way, now owned by Phil Y on WD.

[Cressy Snr]

The insides:

Looks like you built it from a Transcendent kit!

Told you it was "Rozenblit neat"

[Cressy Snr]

That Hotrox wire looks good. Thanks for the link. Looking at your photo on HFS, it appears that your cover is not sitting properly onto your amps top plate. Is it resting on the top of the Tx? I was very careful that my diy cover made no contact with the Tx in any way. Even then, I ran an earth wire from it just to be certain. My KaT88 is still working well in this way, now owned by Phil Y on WD.

No, it isn't on top of the transformer.
Yep, that Hotrox wire is excellent stuff. It's used in guitar amps. I also used the green pushback wire for the 13E1 AC heater runs. There are a few guitar amp parts in the amp. The white, Mallory polyester caps on the driver stage PCBs are excellent sounding and cheap as chips.

[Ray P]

I'm glad the PCBs worked out Steve, I always have a nagging doubt about my layouts...

If anyone else is interested in going down this route I have a small number of spare boards available.

[Cressy Snr]

I'm glad the PCBs worked out Steve, I always have a nagging doubt about my layouts...

If anyone else is interested in going down this route I have a small number of spare boards available.

The PCBs are great Ray. I'm glad you did them and were kind enough to let me have some. I don't think it would have been possible to get the dense, compact layout without the PCBs I'm pushed for space to house the system and if the chassis had been any bigger, the OTL would have been difficult to accommodate on the TV unit.

I owe you a pint at Owston.

[Ray P]

Thanks for the positive comments and the offer Steve, you're a gentleman!

I've just had a browse of your build thread on HFS and nice to see more positive responses to your project. I do like your final build, it looks really nice, especially in the context of your speakers etc. and the colour of you transformer cover is super. I don't have the imagination to be as adventurous as you so the aesthetic elements of my builds are 'safe'.

Is the transformer cover on the HFS photo the cake tin one or have you already found a saucepan?

[Cressy Snr]

The cover on HFS is the cake tin.

[Cressy Snr]

Now the amp is finished, here is the schematic:


Schematic shows a number of changes listed below

• Feedback resistor changed from 6K8 to 7K5

• First stage coupling cap from 1uF to 0.47uF

• Second stage grid resistor now 470K (some datasheets say 300K max, some say 500K; you pays 'yer money etc)

• CCS chip in cathode of output stage changed from TL783 to LM317HVT because of low voltage issues discussed earlier

[Cressy Snr]

Rest of power supply details:

[Cressy Snr]

Rest of power supply details:

Fecking electrolytic caps were upside down FFS!
The bigger schematic will have to do.

[Cressy Snr]

Decided I'd better actually measure some DC conditions last night. On completion of the boxed up amplifier, I'd thrown the HT switch and it played, so I just got on with listening to music through the amplifier.
Anyway, everything checked out nicely. The cathodes of the 13E1 were at 14.25V on the left one and 15.12V on the right, with about 475mA through each valve. In complete contrast to the TL783 aspirated cathodes of the breadboard, these voltages were rock solid; not a sign of any movement once the valves had warmed up.
The LM317HVT is therefore my choice of current regulator if you choose the 13E1 as your single output tube for an STSEOTL amplifier, and are too lazy to design a mosfet cascode.

I'm pleased with this design. Now the wrinkles have been ironed out and the current reg changed, I think it performs beautifully, giving a smooth, fast, detailed and controlled musical presentation. Couldn't ask for much more really.

[Cressy Snr]

I think the boxed up OTL been running long enough now not to be about to blow up, so this afternoon, I've been doing the final construction job of bypassing the output capacitors. It says 6.8uF on the schematic, but I'm buggered if I can find any of the four I allegedly have.
So improvising a bit, I used the best alternatives I had, as the bypasses. These are a pair of big, 600V, 0.47uF, Jupiter, Red Astron "molded" guitar amp capacitors across the cheapo nonedescript 6800uF 63V main output caps. I'd used the Jupiters previously in the pink 2A3 SET to give the a nice fat vintage tone I like for my '60s music.

Fookin 'ell them Jupiters are great on bypass duty. Nice vocal tone, good treble speed and midrange clarity, all mixed up together in just the right proportions for my aging lugholes. No nasties IOW.......Niiice....

[Cressy Snr]

And a couple hours down the line and the OTL is putting out some fab tone. These Jupiter Astron caps have not been used for a couple of years, so I suspect, they needed a thorough warming through in order to show once again, their true colours. Well they certainly get warmed through in this amp .
The sound has really fleshed out now. I'm getting a lovely, full fat, saturated sound. The last thing I could call this OTL is arid.

It's doing the "King Tone" thing like a champ.