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Old 14th September 2012, 04:53 PM   #531
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I thought I'd piggy back this thread to say thanks to Rod for the heater supplies. They work a treat. I havn't been able to comment on the sound yet as the 2 x 0-9v transformer I had in the bit box sounds like a pneumatic drill so I'm in the process of swapping it out for a toroid. It's difficult to appraise the silence with all that buzzing.

Anyway with all the talk of delayed HT I thought I'd mention this anyway:

Vitalstates - SV572

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Old 24th September 2012, 08:02 PM   #532
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Assuming I use 2 Rod Coleman's regulators for 2 DHT output triodes. Do I need
a) separate xformer windings + rectifier bridges + some C filters for each triode or
b) one winding and separate rectifier bridges + C filters for each triode?
I am afraid that in case b) there will be crosstalk between cathodes. Am I right?
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Old 25th September 2012, 05:41 AM   #533
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Quote:
Originally Posted by yagoolar View Post
Assuming I use 2 Rod Coleman's regulators for 2 DHT output triodes. Do I need
a) separate xformer windings + rectifier bridges + some C filters for each triode or
b) one winding and separate rectifier bridges + C filters for each triode?
I am afraid that in case b) there will be crosstalk between cathodes. Am I right?
Hi, Yes, There is a risk of crosstalk, you are right. Please use separate transformer winding and rectifiers for each DHT.

For the best possible solution, a separate transformer is recommended - if the transformer is shared, cross-coupling of rectifier current pulses can increase the overall noise.
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Old 25th September 2012, 05:56 AM   #534
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Quote:
Originally Posted by vitalstates View Post
I thought I'd piggy back this thread to say thanks to Rod for the heater supplies. They work a treat. I havn't been able to comment on the sound yet as the 2 x 0-9v transformer I had in the bit box sounds like a pneumatic drill so I'm in the process of swapping it out for a toroid. It's difficult to appraise the silence with all that buzzing.

Anyway with all the talk of delayed HT I thought I'd mention this anyway:

Vitalstates - SV572

Ed
Hi Ed, Thank you for your kind comments!

when searching for a Filament transformer, please be careful with the quality and construction. There is a big variation of leakage capacitance between primary and secondary windings, and we need the lowest possible value here, to prevent (usually common-mode) noise entry.

Toroidal trafos are not the best performers, sad to say. The capacitance of these may be as high as 1nF, and often the core can't be grounded.

Dual-bobbin [aka split-bobbin] EI types are much better, and I measure 30 to 50pF using Industrial Control-Panel transformers from the UK supplier JMS

1 PH Trans

Most countries have a local maker of industrial trafos, and their customers also like split-bobbin construction, because of better isolation (breakdown) quality. In Italia, the equivalent company is Ideomat Italia Srl, at Modena. I am sure that there are many others.

The other reliable supply of dual-bobbin EI is from Hammond: the 266 series.

Hammond Mfg. - Power Transformer - Dual Primary / Dual Secondary (266 Series)

Regardless of the heating method (or Regulator), the transformer is important quality for filament heating, please choose carefully!
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Old 25th September 2012, 07:09 AM   #535
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Quote:
Originally Posted by Rod Coleman View Post
Hi, Yes, There is a risk of crosstalk, you are right. Please use separate transformer winding and rectifiers for each DHT.

For the best possible solution, a separate transformer is recommended - if the transformer is shared, cross-coupling of rectifier current pulses can increase the overall noise.
Thanks Rod. As I have little room for next xftmr, I will use existing 2 separate 6.3V (*230/220) 3A windings and voltage doublers instead of rectifier bridges.
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Old 25th September 2012, 07:31 AM   #536
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Thanks Rod. As I have little room for next xftmr, I will use existing 2 separate 6.3V (*230/220) 3A windings and voltage doublers instead of rectifier bridges.
A doubler should give good results!

The attached PSUD file uses 6,3V 3A trafo to generate 11V - enough for 6B4G. The rms current in the trafo secondary is 3A.

With a 6,3Vrms 4A trafo, we can generate 10,5V dc using a similar circuit, and feed a 300B regulator.
Attached Images
File Type: jpg Doubler6V3_3A_6B4G_PSUD.jpg (87.8 KB, 531 views)
Attached Files
File Type: zip Doubler_6V3rms3A_6B4G.zip (326 Bytes, 40 views)
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Old 25th September 2012, 07:46 AM   #537
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Toroidal trafos are not the best performers, sad to say. The capacitance of these may be as high as 1nF, and often the core can't be grounded.
Hi,
What about toroidal trafos with a grounded electrostatic shield between the primary and the secondary?
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Old 25th September 2012, 07:49 AM   #538
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Hi,
What about toroidal trafos with a grounded electrostatic shield between the primary and the secondary?
These high quality trafos should work very well - they are designed to tackle the weakness of the standard consumer-quality toroidal: with the cheap toroids, the common-mode noise is very bad.

The measurement that really matters: effective capacitance from primary to secondary.
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Old 25th September 2012, 08:05 AM   #539
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Glad to hear that. I have just ordered custom, electrostatic shielded toroids for my GM70 project... I'll measure the capacitance when I get them.
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Old 25th September 2012, 08:44 AM   #540
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Quote:
Originally Posted by Rod Coleman View Post
A doubler should give good results!

The attached PSUD file uses 6,3V 3A trafo to generate 11V - enough for 6B4G. The rms current in the trafo secondary is 3A.

With a 6,3Vrms 4A trafo, we can generate 10,5V dc using a similar circuit, and feed a 300B regulator.
Glad to hear that!

Actually it is 6,58Vrms, as it was built for 220V primary. Now in PL mains voltage is 230V, thus 6,3V*1,045
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