Gas tube regulation

[Paul Birkeland]

The PT-5 has plenty of voltage and current.  For the high voltage, use a full-wave bridge rectifier into one of the stock 220uF caps, then the 157G, then at least one 220uF cap (maybe 2 in parallel). This will leave you with ~165V of raw B+, which is plenty to light up an 0C3.  I'd set your dropping resistor for 50mA, so 165V-105V=60V, 60V/0.050mA=1200 Ohms.

For power, 1200 Ohms * (0.050mA^2)=3 Watts, so use a 10 watt resistor. 

If you used a voltage doubler, this resistor would need to be quite large.

For the heater supply, I'd use a bridge of the 1N5818 diodes, then a 10 Ohm/5W Rheostat wired as an adjustable resistor, then a 10,000uF cap.  Start with the rheostat at half its rotation, plug your two tubes in, then use your meter to dial the voltage to 5.9V. 

At some point, it becomes easier and less expensive to build an Eros

[gstew]

Paul,

Thanks for the info... it will be invaluable.

One question on the filament supply... I was intending to reuse the stock 1N5818's & 10kuf cap and then go into a Linear Tech regulator (likely one LT3080 per tube, but I could go with a single LT1083 instead for simplicity). I figured if it is good enough for the Eros, it is good enough for my Seduction. Bad move?

Then on doing this rebuild instead of just getting an Eros...

1. I have a 5.5" x 12"-14" space available. My Seduction stock won't fit, but I can restructure it to do so. Looking at the Eros, I don't see any easy path to fitting it in that space.

2. I already have the Seduction and this won't cost much in parts (About $200 for the iron and the cast ally boxes versus almost $740 for an Eros... and I need to cast boxes to repackage it for fitting in the available space anyway).

3. I'm already in build-mode, doing a couple of solid-state phono stages to try too... but both are current input for LOMC's only, this turntable has an arm known for being a challenge to setup correctly (Older Well-Tempered Classic), and I don't want to risk a higher-buck LOMC while I"m learning the arm. This build flows naturally with the other two.

Again, thanks for the info and the advice.

Greg in Mississippi

[Paul Joppa]

A linear regulator is good. Set it up for 6.0 volts, not 6.3 - this gives a longer life and potentially less noise as long as the plate current is low, as it is in Seduction.

We tried the LT3083 (3-amp version of the 3080) and couldn't get the noise (hum/buzz) down; I suspect the higher impedance voltage setting node is sensitive. Just a word of caution; we're still experimenting but no answers yet. The 1083/4/5 series have behaved themselves. Just read the notes in the spec sheet, especially about using the right kind of capacitors.

I had forgotten the earlier experiment with the PT-1. PT-5 into a FW bridge should give slightly more than PT-1 in FWCT, so a choke-input supply is possible if you use a current source to feed the shunt reg gas tube. (With a resistor, the current becomes a strong function of the power line voltage, so I don't recommend it.)

[gstew]

Paul,

Thanks. Sorry, I didn't say before, but I will be using a current source to supply the 0C3... I have a couple of the BH CCCCS kits from back in the day when I thought I could convert my Seduction to dual-mono.... until I realized the clever design ya'll put into your Seduction current source upgrade.

Thanks for the tip on the LT3083. I didn't even know about that variant... will have to get some. I use the LT3080 to replace LT1083's in some audio-ish applications and found it a nice upgrade there. Pity! I'll stick with the LT1083/1085 line then.

As I said, the PT-5 is on order. BTW, roughly when might that order ship, holidays & such?

Finally, got a bit of a disappointment last night... I had purchased some caps for upgrading the RIAA a few years back, but never put them into my Seduction as I didn't have my vinyl setup running then. I got the bag out & checked them on my trusty B&K & all were too far away from the target values to use. So I think I'll go the route of the AMTRANS polyprops from Parts Connexion... parallel 2 5600pf for the .0112uf value and 4 8200pf for the .033uf value. I'll get a few extra of each value so I can make 1% combos. Of course, their holiday shutdown means I won't see these any faster than the end of next week! More delays!

Again, Thanks!

Greg in Mississippi

[saildoctor]

Part of my goal in my own build was to add the 0C3 but keep it all within my existing Seduction chassis with the same tranny.  Well... actually I think if I had to explain why I needed another box to power the first box my housemate may have tried to smother me as I sleep.  Ha!  That's great that you're going for it - bet it will be super quiet!

[gstew]

Part of my goal in my own build was to add the 0C3 but keep it all within my existing Seduction chassis with the same tranny.  Well... actually I think if I had to explain why I needed another box to power the first box my housemate may have tried to smother me as I sleep.  Ha!  That's great that you're going for it - bet it will be super quiet!

LOL!

My housemate is a saint about my hobbies... and you'd agree if you saw how much my different projects and sprawling stereo have taken up space in our home!

We'll see about the quiet. This is for my smaller, downstairs system where it shares a shelf with the turntable. Whenever I get the main, upstairs system going again, the phono stage has it's own stand and there's plenty of room for the full-sized Seduction or larger.

Part of the reason for the repackaging is to fit it into a space.  only 6" wide or so... but also, it sits next to my computer music server. While I've done a lot of mods to that to reduce conducted & radiated EMI/RFI, it will be only a few inches away. I know I may have to power down the server to play records... I can live with that. It may be I only have to power down the highest-polluting item, the small screen, which has its own supply and can be powered off by itself. But part of the reason for the re-boxing is to better shield the whole thing.

One issue I'm grappling with is how to deal with mechanical vibrations. The cast ally boxes ring... they'll get damped. Then I'm rebuilding the Seduction active circuit on a piece of Corian... that will get damped too and it'll have a suspension using Herbie's Audio Product material. It's somewhat of an experiment, but a fun one... and having your gas-tube regulator upgrade to go in at the same time is just another excuse for doing it! Thanks for publishing that!


Greg in Mississippi

[Paul Joppa]

...So I think I'll go the route of the AMTRANS polyprops from Parts Connexion... parallel 2 5600pf for the .0112uf value and 4 8200pf for the .033uf value. I'll get a few extra of each value so I can make 1% combos. ...

Another way to go is to use 0.030uF and 0.010uF caps, changing the resistors 66.5K to 75K and 9.64K to 10.7K. Precision caps are often available in only a few values, but 0.010uF is usually one of them, and you can parallel three of them to get 0.030. Sometimes you get a price break for 10 caps, so you throw out the worst two and sort the rest. The target is actually 0.0297 and 0.01011, and 73.7K, as long as you're sorting...

[gstew]

Paul,

Thanks, that's very helpful. It'll give me some flexibility in cap selection.

I'll be using 6N1Ps... I assume that these values don't change, but is the change of the RIAA termination resistor from 1M to 500K affected?

Also, I have .033uf and .011317uf as the nominals for the stock Seduction RIAA values... those right?

Again, and as always, thanks!

Later!

Greg in Mississippi

[Paul Joppa]

Paul,

Thanks, that's very helpful. It'll give me some flexibility in cap selection.

I'll be using 6N1Ps... I assume that these values don't change, but is the change of the RIAA termination resistor from 1M to 500K affected?

Also, I have .033uf and .011317uf as the nominals for the stock Seduction RIAA values... those right?

Again, and as always, thanks!

Later!

Greg in Mississippi

Yes, I'd change the load resistor to compensate for the 6N1P's higher plate resistance.

Take 60pF off of C2 (0.011257uF) - 50pF for Mr. Miller, and 10pF for wiring, socket, etc. capacitance. If you need to be REALLY picky! I get 66pF total for the 6N1P, according to the US Svetlana data sheet - net 0.011251.