JoaMat

Regarding GRHV regulators. What’s the minimum voltage differential/headroom for the GRHV to work properly?

Well, I use some old DIY T2 supplies for all my amplifiers. For LV and filament transformer I have the following windings 15V + 15V / 0.5A (center tap) 6.3V / 4A 6.3V / 4A 6.3V / 1.5A 6.3V / 1.5A You don’t want to use same winding for small and output tubes. Separate windings for channels. So total four filament windings. Demands for HV is 60mA for output stage and 20mA for input. With +220V supply you I suggest 195V/0,06A 320V/0.18A 365V/0.18A \\135VA Without +220V supply, feeding input positive via 20k power resistor, I suggest 320V/0.24A 365V/0.18A \\143VA Calculations are based on 50V headroom and current factor of three (some builders may want another factor). Reservation for errors!

Lazy engineer/designer

Frankly I expected OP27 to fail sooner or later. I’ve had several OP27 failures, only the offset servo – no balance servo failure so far. I hope that the OPA197 is more robust. I’ll use OPA197 from now in new builds… as long as they work properly…

So – now it has failed (couple of days ago), both outputs at +HV. First I put a 650R resistor cross Q10 collector/emitter which brought offset voltage down to +60V increasing to about +90V when warm. Changed the failed OP27 to OPA197 today and now it’s working again.

Four Gold Lion KT77 in a mini T2. G3 connected to plate on PCB. It rocks Beautiful!

If interested in the story of good old tubes, I recommend Guide to the EL34/6CA7 by Pasquale Russo. Also some information on the KT77. 365 pages of interesting stuff.

Not sure which one of all Kevin’s designs the “all tube Grounded Grid” is. But in mid-2017 both members congo5 and MattN have built what seems to be something similar to Kevin’s KGSSHV-TUBE- SANDWICH – ECC88 input and EL34 output tubes. Ref. https://www.head-case.org/forums/topic/12949-stax-t8000-clone-well-sorta/

Happy New Year!!!

Carin Lundin - From Dusk to Dawn

more Down the Road...

Bach through Icelandic fingers.

Well, I did start with a layout of a regulator board with some smd parts. A sop-4 ssr for relay… … but it all stalled. The to-220 regulator probably needs a heat sink and the layout has to reworked – it's just an early draft. But so far I stick with the EML V20B to EL34 adapters I have. Maybe you should make your idea of adapter public here on Head-Case. I think it’s a very elegant way to make it possible to use either EML tubes or EL34.

I’ve no knowledge about Justin’s latest project so no point asking me. I’m very exciting in this new amplifier - as probably most Head-Case members are. P.S. Some years ago Kevin published an amplifier layout for EML DHT tubes. Crazy as I’m I bought some EML tubes and made adapters for the tubes to be used as replacement for EL34/6CA7.

Said to be recorded by Italian Columbia on 26 78-rpm sides. Transferred from American Columbia and Italian Columbia pressings by Ward Marston.

B. B. King with Gladys Knight, Clapton, Collins and other friends. Illegally downloaded years ago. MP3 164 kbps – who needs highres?

Happy Birthday!

Yes, heat sinks and front/rear panels are from modushop.biz. Brackets and aluminum plates for top/bottom covers from local shops. Drilling, tapping and other crafting done in kitchen.

Today I joined the Qobuz family. They don’t like Sweds but with a little from NordVPN they think I’m an English Brexiteer. Found this on Qobuz - in flac 96kHz 24bit: Esbjörn Svensson Trio - Live in Gothenburg

I have been using Roon for some time now and I really like it. Roon points at (my own library and Tidal) 300+ tracks of Bye Bye Blackbird – and Sarah Vaughan did one in Tokyo, 24 September 1973?. 2CD - great album.

The new T2 has behaved in a good manner for a whole month. Now qualified for old good tubes... ...Amperex Bugle Boy to the left and Brimar to the right.

Great! …then I found this...

FedEx came an hour earlier than expected. One amplifier has now “new” op amps OPA197. The other has new OP27, one channel with 10K instead of 25K at -input pin. So now I just have to wait and see. I expect the OP27 with 25K resistor to fail sooner or later. For the rest - wish me luck!