Remember These?
#511 Re: Remember These?
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?
Sorry, I couldn't resist!
#513 Re: Remember These?
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.
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#514 Re: Remember These?
Told you it was "Rozenblit neat"
Last edited by Cressy Snr on Tue Mar 26, 2019 11:27 pm, edited 2 times in total.
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#515 Re: Remember These?
No, it isn't on top of the transformer.Greg wrote: ↑Tue Mar 26, 2019 10:35 pm 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.
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.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#516 Re: Remember These?
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.
If anyone else is interested in going down this route I have a small number of spare boards available.
Sorry, I couldn't resist!
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#517 Re: Remember These?
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.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#518 Re: Remember These?
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?
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?
Sorry, I couldn't resist!
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#519 Re: Remember These?
The cover on HFS is the cake tin.
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#520 Re: Remember These?
Now the amp is finished, here is the schematic:
Schematic shows a number of changes listed below
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
Last edited by Cressy Snr on Sat Mar 30, 2019 12:28 pm, edited 6 times in total.
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#521 Re: Remember These?
Rest of power supply details:
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#522 Re: Remember These?
Fecking electrolytic caps were upside down FFS!
The bigger schematic will have to do.
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#523 Re: Remember These?
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.
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.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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#524 Re: Remember These?
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....
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....
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#525 Re: Remember These?
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.
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.
Sgt. Baker started talkin’ with a Bullhorn in his hand.