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ZKIT 1 power supply upgrade questions (Read 3269 times)
chris_m
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ZKIT 1 power supply upgrade questions
04/30/10 at 02:36:32
 
Hi,
I've been listening to my completed ZKIT 1 for over a month now and continue to really enjoy it.  I plan to commit it to a steel chassis so I don't have to worry about electrocuting our cats while listenign.  I'm considering some of power supply upgrades and seek some information.

Q1. It looks like the power transformer readily allows me to upgrade to 5U4 tube rectification.  Am I right and would I simply tap off the output tube bias (A) before the 1K dropping resistor instead of after it if I do this?

Q2. SE tube amps typically benefit from choke regulation.  Is there a choke spec I could utilize if I'd like to incorporate this?  Is there a Decware choke that can be purchased for this purpose?

Thanks,
Chris
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chris_m
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Re: ZKIT 1 power supply upgrade questions
Reply #1 - 05/13/10 at 00:07:31
 
Well, I went ahead with inserting a 5U4G in place of the diode full wave, connecting the yellow/black wire to diode side of the 1K 6W resistor. This should match how it is depicted in the SE84C schematic from the product info page. It works of course but there is a drop in voltage.  There are sonic differences too naturally.

With diode full wave:
voltage point A: 342V
voltage point B: 305V

With 5U4G full wave:
voltage point A: 310V
voltage point B: 279V

The differnce in voltages seems consistant given the specs of a 5U4G vs. a 1N4007 diode.

The question I don't have an answer to is how the 320-350V range suggested for the B+ reading (same as voltage point A) can be that high with the rectifier.  The cathode voltage with the 5U4G is 9.3V which is also below the 9.5-12V recommended range.

So I am left to consider the possibility the ZKIT 1 power transformer is not the same as used with the SE84C unless the schematics and the component values are not current.  I had another 5U4G to try as well.  The voltages were with in a volt of the first rectifier tube.
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dank
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Re: ZKIT 1 power supply upgrade questions
Reply #2 - 05/14/10 at 13:30:23
 
I have always wondered why the Zkit1 was set so close to the absolute maximum spec of the output tube...now I know!

I'll bet the rectifier tube was replaced by silicon diodes (as a cost savings measure) and no other circuit changes were made.  This resulted in a plate voltage of 346 on the output tubes (342 in your case) instead of 305 in the Zen SE84C.  Being that the cathode is around 10v, this yields a net plate voltage of 336 for the Zkit1 and 295 for the Zen.  In my 6P15P data sheet it lists the maximum permissible plate voltage at 330...always wondered about that.
Obviously the tubes can tolerate more, as my Zkit1 has had further mods to it that boost this voltage even higher, but I suspect tube life suffers, and maybe sound quality changes....OR MAYBE HUM GETS LOUDER!!!!!


Dan  
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chris_m
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Re: ZKIT 1 power supply upgrade questions
Reply #3 - 05/14/10 at 21:50:57
 
Dan, that makes a lot of sense to me.  I didn't know the SE84C could have a plate voltage of 305V.  I've never had that amp to examine and the schematic on the SE84 info page lists it higher.  At 305V those tubes should last a good while.

I would guess with higher the B+ goes higher the plate currents and I suspect the hum gets louder.  In fact, the hum filtering probably is tuned closely to the current requirement.  

I am tempted to consider a choke with a little more elaborate RC filtering to raise the B+ at the plate while still limiting hum to decent levels.  But I think Steve's design is highly optimized and it might be difficult to pull that off.

Chris
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chris_m
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Re: ZKIT 1 power supply upgrade questions
Reply #4 - 05/16/10 at 01:26:40
 
FYI, I continue to listen to the 5U4G in place of the full wave diode pair.  I reported the B+ voltage drops which was expected but does not match documentation.  

FWIW, with the 5U4G I think the backgroud is quieter, darker with diode rectification. With the 6N1P the lower voltage does seem to reduce the speed and dynamics but I put a 6922 in and quite honestly it sounds awefully decent.  Lots of detail.  Very engaging.  The speed seems to be restored with the 6922.

I considering a multi-section RC filter with lower over all resistance to up the B+ a little and see if I can get back to preferring the 6N1P.  

Has anyone else tried the 5U4G with the ZKIT1?  I would be interested to hear your experiences.

Chris
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Crazy Bill the Eel Killer
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Re: ZKIT 1 power supply upgrade questions
Reply #5 - 05/20/10 at 19:21:24
 
Hello Chris,
I haven't got much time now, but I've played around extensively with my SE84CSEX and here's a few things you could try.

If you're committed to RC filters in the PS, figure out what R value you need and then use a dbl PI filter ( CRCRC) with the total R value needed divided between the two resistors in the PS.

Also, I don't know what cap values are used, but try lowering the first cap value  and then increasing up the line i.e.  15uf,R,40uf,R,80uf. The lower value first cap will decrease the charging currents through the rectifier ( lower noise ), and the increasing values will lower PS ringing and make it more stable.

Plus adding additional RC sections increases the efficiency of the filter far better than increasing either the R or C values.

Only caveat is lowering the first cap value will also lower your B+, so you may have to play with the cap values and the R values to fine tune it. But that's half the fun.

Plus, if you've got the room, you must get as many of the electrolytics out as possible, and put ASC motor runs in instead. HUGE difference.

Have fun and let us know what you decide to do.

Cheers,                Crazy Bill
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chris_m
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Re: ZKIT 1 power supply upgrade questions
Reply #6 - 05/21/10 at 13:05:10
 
Hi Bill,
Thanks for your response.  This is very useful information. The multi-section RC filtering is something I have been thinking about but I am considering the reduce R total to increase the B+ for running off of the 5Ru$ vs. the FW diode. The voltage drops from 342V to 310V at the OPT on my kit.

Question: Can you quote the voltages you get at the B+ connection to the OPT and the plate/cathode connections of the signal tube?

I am not at all familiar with ASC motor run caps.  I look forward to researching these.  I will need to plan for a larger chassis if I use them it looks to me.

Thanks again,
Chris
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Crazy Bill the Eel Killer
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Tubes Rule !!

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Re: ZKIT 1 power supply upgrade questions
Reply #7 - 05/24/10 at 15:00:55
 
Hello Chris,
sorry it took so long to get back to you, it's been a crazy weekend.

I'm sorry but I can't check the voltages you need, as the amp is in pieces. I'm quessing, and IIRC, its was 300-305 at the plate, and just short of ten volts dropped across the cathode resistor. But those are guesstimates. If I were you, while I'm still breadboarding, I would hit the output tubes at both voltages you are considering, and give a good listen. Let your ears decide.

One thing I can tell you with certainty is that you are not hearing the 6n1p at anywhere near its true potential. Even though they and the 6922 types are touted as replacements except for the increased heater current of the 6n1p, their operating characteristics are so vastly different that one operating point will not be optimal for both tubes. Steve is definately hitting the tube in a far better region for the 6922 types ( around 90 volts @ couple ma, IIRC ). This is definately a very suboptimal operating point for the 6n1p. Try hitting the 6n1p w/ 200 volts @ 10ma ( 200 ohm cathode resistor ), and you'll never look back ( IMHO, very biased as they are my ears doing the listening ,YMMV ).

I'm also not able to give you any suggestions on actual power supply R values to achieve those voltages, as I went to IT coupling so my PS configs are vastly different than what you would need.

One last thought for now. Before you decide on a final config, make sure you listen to the 6922 @ about 6 ma or so, i.e. 100 volts w/ 480 cathode resistors. To my ears a much sweeter sounding point for that tube.

Have fun playing. There's lots of other stuff to try, but you shoulf breadboard the amp w/ stock values first and then listen to get a good feel for the sound of the amp. Then change one thing at a time and listen some more. Eventually you'll find the combo that floats your boat the highest.

Let us know how it turns out. Moving to the tube rectifier was a very good start.

Heres a link for the ASC caps:

http://www.partsconnexion.com/capacitor_film_asc.html

Do a search over on the Hawthorne forum for ASC caps. Theres some great reading from Eddie V.

Cheers,                   Crazy Bill
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