another Big One....:)

[Bandersnatch]

hey-Hey!!!,
I have had no new amps created in more than a year. I think it is time to build another. This one will use the big TV sweep tubes, 6LF6 for example. Run Class A, pentode mode with shunt regulated screens and of course, no loop NFB.

So far, it looks like a two chassis affair, PS on one, B+ on the other. Front end and B+ run from the B+ and g2 with their own supply feeding a shunt regulator. Type 866 for B+, and type 83( maybe 816 ) for the g2. I've been looking at the big Antek torroids at 500-0-500 level for rectified DC near 400V.

6k6 a-a will deliver class A operation with around 100 mA/tube idle. I have several other OPT's to play with, 5k with 10% CFB the Chicago BO-14 for starters, and some Peerless 20-20 Plus to continue the project.

I can't help considering the clip-lead and plywood breadboard.
cheers,
Douglas

[audiowize]

What kind of shunt reg will you run? I'm currently in the chassis design phase for a 6252 transmitter PP amp driven by compactrons with an IT coupled LTP driver fed by a hybrid shunt reg. I'm using two new stock ST-70 power transformers and two Dynaco A-431's for output. Triode wired, this should be a very pleasant amp.

[Bandersnatch]

hey-Hey!!!,
The shunt regulator voltage ref/shunt element is an amplified Zener string. It runs a small BJT NPN as an intermediate amp and a P-channel MOSFET as main pass element. Output Z is about 1% of the Zener string, and its AC performance should be slightly better. I should probably put up a drawing...
cheers,
Douglas

[audiowize]

Yeah, draw it up! I'm using a current source feeding the plate of a beefy triode and a TL431 as the voltage regulator. Unfortunately, I will also likely end up with a string of Zeners to pull the voltage down while the tube warms up (to keep the current source solid state devices in spec)

[jon_010101]

Please do some tests with some 3B28s, too! I have 8 of 'em waiting for my future 813 SEP project. Curious to see how they compare noise-wise / drop-wise / sonics-wise ... despite the lower toxicity and inferior weak purple glow.

[Boris_The_Blade]

Sweet! Another big project. Hopefully you got a big stash of them 6LF6, I hear they're quite pricey. Please take lots of pics!

Good luck!

[Bandersnatch]

Originally posted by jon_010101
Please do some tests with some 3B28s, too! I have 8 of 'em waiting for my future 813 SEP project. Curious to see how they compare noise-wise / drop-wise / sonics-wise ... despite the lower toxicity and inferior weak purple glow.

hey-Hey!!!,
I should be able to run nearly any 2.5 V recitfier. One of the big benefits of the Hg tubes is their need for delay. So everything will get the same delay and thus avoid any issues with g2 voltage comming on ahead of the plate's supply.

All that care does nothing for the portability issues...I suspect it will be another near-quarter-ton amp.

As far as a supply of finals...rest assured I've either got a large sack of them or a sure cheap supply...
cheers,
Douglas