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 jhstewart9 11th September 2019 02:37 AM

What Benifit does Returning the Cathode Cap to B+

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Looks like not much, the AC current thru the cap remains the same whether returned to Common or B+. But return to the B+ brings with it the introduction of PS Ripple into the signal path.

 PRR 11th September 2019 03:27 AM

Do you have 7.5k load on 7.5r winding?

 disco 11th September 2019 09:13 AM

From your simulations the conclusion can be drawn PS ripple plays a greater role when the cathode gets decoupled to PS instead of ground. With actual numbers (ripple < 20mV) the difference would be small. Though, on micro levels some influence from power supply AC exists.
To isolated the input stage from PS, I replaced the anode load with a CCS set for 5mA. Next I'll have a look at the 50 workpoint and alter the PS setup as the 10 and 50 share the same PS, isolated by just the impedance of their loads. Some more cyphers to follow.

Rough Estimate of Damping Factor, taken from 8Ω tab.
1,00V 1KHz in 8R resistor, output without load= 1488mVrms.
Internal resistance ΔE= 0,488V ΔI= 0,125A 0,488/0,125= 3,90Ω
According to the rough estimate DF= 8/3,9= 2

 jhstewart9 11th September 2019 01:54 PM

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Quote:
 Originally Posted by PRR (https://www.diyaudio.com/forums/tubes-valves/342283-50-triode-amp-post5911206.html#post5911206) Do you have 7.5k load on 7.5r winding?
The ripple voltage set is arbitrary, probably much better in practice.:)

 disco 11th September 2019 06:27 PM

5K in place, bass seems better controlled but less deep. Dissipation is 22W, tomorrow I'll take some measurements.

I wonder what the limit is for the interstage. It's a C-core with enamelled wire, poured in with silicon compound. The power supply is at its top now. I could exchange the tranny for a 1000V CT unit and employ a thermal rectifier...

 jhstewart9 12th September 2019 02:53 AM

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Under ordinary operating conditions all triodes have about the same damping factor. Simply depends on the relation between the plate resistance & the OPT impedance reflected from the load. Then the wire resistance in the OPT, lower is better. This article explains it well.:)

 PRR 12th September 2019 03:12 AM

Quote:
 Originally Posted by PRR (https://www.diyaudio.com/forums/tubes-valves/342283-50-triode-amp-post5911206.html#post5911206) Do you have 7.5k load on 7.5r winding?
Quote:
 Originally Posted by jhstewart9 (https://www.diyaudio.com/forums/tubes-valves/342283-50-triode-amp-post5911583.html#post5911583) The ripple voltage set is arbitrary, probably much better in practice.:)
That is not what I was asking.

I realize the ripple source is arbitrary.

But a 1000:1 mis-fit of load to tube (through transformer) radically changes the ripple around the loops, masking the effect you are trying to show.

 disco 12th September 2019 12:12 PM

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Comparison of the two OPTs learned there's not much difference to be had with this particular loudspeaker. Below is a chart for measurements up to 10KHz, the horizontal scale is not linear.

Further refinement could be to investigate HF behaviour as Tango XE-20S is sensible for ringing at high frequencies. A RC combination at the 50 anode might work.

From the ancient Sylvania manual the thought arose 3K5 was a suitable load for 400V plate voltage. 5K seems slightly better wrt damping and distortion at the expense of half a watt output power. Remember, Platevoltage == Vak.

The power supplies is built from parts at hand, you would certainly do better than this designing your own.

It's a lovely little amp that deserves a good loudspeaker as I found out. Perhaps a Lowther or Philips 12 inch broadband unit. Bright emitter 10 tubes have a shorter life span (1500 hours) than the original oxide coated type (5000 hours).

 jhstewart9 12th September 2019 05:37 PM

5 Attachment(s)
Quote:
 Originally Posted by PRR (https://www.diyaudio.com/forums/tubes-valves/342283-50-triode-amp-post5912273.html#post5912273) That is not what I was asking. I realize the ripple source is arbitrary. But a 1000:1 mis-fit of load to tube (through transformer) radically changes the ripple around the loops, masking the effect you are trying to show.
OK, got it. I missed that completely. I will attribute that to rushing too much..........or just too old. Lots going on here as usual, manual labor, cutting the dead ash down, Etc.
So here is the series of measurements again, this time the load corrected. The bottom line still holds, returning the cathode cap to B+ is not the best plan.:)

 PRR 13th September 2019 01:28 AM

> returning the cathode cap to B+ is not the best plan.

Yes, for ripple rejection. Cap to B+ injects ripple to cathode where it amplifies about as Mu, cap to ground doesn't.

Where you find this connection most is old W.E. designs with massive B+ filtering, so that ripple is small in any case.

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