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Old 27th December 2012, 07:09 PM   #11
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Hi!

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Originally Posted by Original Burnedfingers View Post
Would 6DW4B's work also?
Yes!

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Old 27th December 2012, 08:08 PM   #12
chip647 is offline chip647  United States
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Hi!
This is not really correct, the plate dissipation calculates as current multiplied by the voltage drop within the tube. Not the supplied voltage. The voltage drop within a 6AX4 is quite low, depending on current draw maybe 25V.

A supply like this can easily deliver 200mA at 950V

Thomas
Yes, sorry. I though about that after I posted.
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Old 27th December 2012, 09:29 PM   #13
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Hi!



Yes!

Thomas
All things considered which damper tube would be better?
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Old 27th December 2012, 11:33 PM   #14
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Hi!

Quote:
Originally Posted by Original Burnedfingers View Post
All things considered which damper tube would be better?
They seem fairly close to the 6AX4, with probably more current handling capability. I wouldn't have a specific preference. I'd expect them to work quite well like most TV dampers.

Thomas
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Old 28th December 2012, 02:54 AM   #15
wa2ise is offline wa2ise  United States
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The max current spec for the 6AX4 is 1000ma, similar to the 5U4. And a max capacitor rating is related to the max current spec, so what the 5U4's limit is should also be a reasonable approx max for the 6AX4.
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Old 31st March 2013, 01:03 AM   #16
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The max current spec for the 6AX4 is 1000ma, similar to the 5U4. And a max capacitor rating is related to the max current spec, so what the 5U4's limit is should also be a reasonable approx max for the 6AX4.
I use a pair of 6AX4GT tubes with a pair of silicon diodes in series before each anode, and they quite happily drive 150uF of capacitive loading at 370 volts. The voltage drop across the 6ax4 tubes is around 25 volts in this circuit which is supplying 200mA
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Old 1st April 2013, 04:41 PM   #17
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Hi Peter,

why the silicon diodes in series? They can only provide some extra peak inverse voltage capability. The 6AX4 has more than enough PIV for a 370V supply.

While it maybe can handle a large cap, I wouldn't want that. If I have to use a cap input filter I try to keep that cap as small as possible. This always yields better results.

Best regards

Thomas
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Old 1st April 2013, 04:53 PM   #18
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Originally Posted by Vinylsavor View Post
Hi Peter,

why the silicon diodes in series? They can only provide some extra peak inverse voltage capability. The 6AX4 has more than enough PIV for a 370V supply.

While it maybe can handle a large cap, I wouldn't want that. If I have to use a cap input filter I try to keep that cap as small as possible. This always yields better results.

Best regards

Thomas
I use around 1000uf cap after the silicon diodes to make the PSU as stiff as possible and as much capacitance after with low esr electrolytics afterwards for a rock solid PSU with a soft start. I follow this with a set of valve regulators down stream for the output and preamp stages each with at lest 100uF of filter on them to lower the impedance of the regulator at HF. This prevents nasty power supply sag even prior to the regulator and after the regulator the filter cap keeps the regulator on track even at high output hi frequency material (eg up to 20KHz). This provides the amplifier the best possible sag-less PSU for ultimate sound quality and performance, and it really works the improvement is amazing. So you get all the slow start properties of a valve rectifier with all the benefits of really steady PSU,
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Old 1st April 2013, 05:01 PM   #19
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Hi!

So this is probably a high power amp, possibly Class AB? I never had an issue with PSU sag in a pure Class A design. So you have a 6AX4 rectifier followed by 150uF and then another 1000uF after the silicon diodes? This will still stress your 6AX4s. But they are some tough tubes and cheap

Best regards

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Old 1st April 2013, 05:33 PM   #20
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Originally Posted by Vinylsavor View Post
Hi!

So this is probably a high power amp, possibly Class AB? I never had an issue with PSU sag in a pure Class A design. So you have a 6AX4 rectifier followed by 150uF and then another 1000uF after the silicon diodes? This will still stress your 6AX4s. But they are some tough tubes and cheap

Best regards

Thomas
The 1000uF is between the silicon diodes and the Damper tubes.

The amp is mostly class A up until the last 10% of output, using 4 pairs of 6AQ5 tubes in parallel push pull.

By having a regulated supply for both the output stage and the preamp stages fed from a rock solid psu it separates the amp from line voltage drift and makes sure your amp and preamp are running precisely at the voltages you designed them for.

It does take over 20 tubes of varying types per channel but its worth it!
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