6P3S-E Cathode Resistors - diyAudio
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Old 22nd May 2012, 06:59 AM   #1
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Default 6P3S-E Cathode Resistors

I have just about completed assembling parts for an SSE build later this year. My main components are;
Hammond 374BX power transformer,
James 6123HS output transformers (5K),
Hammond 193J choke and
40uF/440v motor run cap.
From forum postings and using a 5AR4 rectifier, I hope to achieve a B+ of about 450v. I have some Russian 6P3S-E's that I thought would be a good place to start. From the forum it is evident that a higher rated cathode resistor, eg 750-820R, would be more suited to these valves. Would this be a sensible choice and is that B+(450v) okay?
In future I would like to move on to using new Tung-Sol 6L6GC-STR's, which would possibly be happier with the standard 560R cathode resistors.
Not being an experienced builder and wishing to keep things relatively simple, any advice would be appreciated.

Lastly, a big thumbs up for Digikey. I e-mailed my order for the majority of the items on the SSE PCB parts list last Sunday evening and in less than 2.5 days my parcel arrived. That's what I call great service.

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Old 22nd May 2012, 03:57 PM   #2
zman01 is offline zman01  Bangladesh
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Still running the Frugel Horn Mk3s?

Your choice of trafos is the same as what I am planning - may I ask where did you get the James 6123HS?

I'm a noob - so somebody else will have to answer your cathode resistor question.

- Zia
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Old 22nd May 2012, 05:36 PM   #3
rknize is offline rknize  United States
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820 is a safe place to start. It should be cold enough for any tube. I'd pick up a few other values, just you can play around with it. I don't know what the Tung-Sol reissues are like. I don't have any experience with those particular tubes.
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Old 22nd May 2012, 05:45 PM   #4
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Hi Zia,

Yes I still have the FH3's, they are great. I had a pair of Fostex 167E's so I purchased plans from Bob Brines and built his FT1600 MkII's. NICE.
I currently have a 0.75 Watt 'Darling' amplifier so I am trying George's SSE for a little more power. Should be good.
I see that you are also thinking along these lines.
There is plenty of good information on the forum and it helped greatly when putting my parts list together.

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Old 22nd May 2012, 06:02 PM   #5
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Hi Russ,

Thanks for the advice. I took a look at your website and the 'binding post' method for swapping cathode resistors would be the sort of solution that I would be looking for.
Could you please tell me how that works for you and possibly provide some additional information on the type of binding posts used?

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Old 22nd May 2012, 06:33 PM   #6
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Hi Zia,

About the James 6123HS output transformers, they came from a guy called Sandy in Taiwan via E-bay. This was quite a while ago and I'm not sure whether he is still trading.

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Old 4th June 2012, 07:55 PM   #7
Alco is offline Alco  United States
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I recently completed a tubelab simple SE and have been listening to 6P3S-E tubes. I like them very much; I can compare them to Groove Tubes KT66 (from china), and Groove Tubes KT88 with the heat sink (I think these are similar to the JJ). I've settled on the 6P3S-E as my current favorites.

my B+ is 455
plate voltage: 443
cathode resistors: 600 ohms 5 watt
cathode voltage left: 34.6 so 23.55 watts Pdiss
cathode voltage right: 35.8 so 24.29 watts Pdiss

These tubes sound darn near as good as the kt88's and consume a lot less power. I've got the amp plugged into a watt miser meter and with the 6P3S-E's I clock 107 watts; with the kt88's it burns up 150 watts !

Also noted with the watt miser is the fact that the 12AT7 I prefer, a nos sylvania 12at7a, uses more electricity than the 2nd best, a phillips jan 12at7wc. The 107 watt setup above is with the Sylvania 12at7a, with the Phillips I clock 89 watts.
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Old 7th June 2012, 11:01 AM   #8
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Hi Alco,

Thanks for the information. The 6P3S-E seems like a good all-rounder. Glad that you are enjoying them.
I have just ordered a pair of Tung-Sol 6L6GC-STR tubes as users have posted that they also get close to the KT88's performance in the SSE.
What method do you use to change your cathode resistor values?
I think I will opt for a ON-OFF-ON DPDT switch to give three values for tube rolling.
rkinze (Russ) has posted helpful advice about switching and he has also included a spreadsheet to assist with the necessary resistor selection.
The forum is a great source of information.

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