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Kit1 Anode Voltage

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Hi all,

I recently bought a Kit1 which I�m very happy with (though I�m very tempted by the monoblocks kit � maybe with a bit more in the bank).

I�m using Western Electric 300Bs and wanted to make sure they aren�t being driven hard. With the guidance of an experienced engineer (who is currently on holiday) I�ve measured the Voltage between Anode and signal ground at 517V. Cathode to signal ground is 88V, making 429V across the valve. The kit1 diagram shows 425V at the 300B anode but I wanted to ask does that refer to the voltage across the valve or voltage anode to signal ground ?

If it�s the latter then the amp is running out of range for the valve. On the other hand if it�s the former then I�m fine. However, I�ve stopped playing it until I�m sure.

Hoping someone can confirm this for me.

Follow Ups:

RE: Kit1 Anode Voltage - Frank E 09:10:56 10/04/07 (8)
Just a few words as I have to run.

517V is way too high for the anode. The B+ power supply should only be putting out 435V +/-. You'll want to check your power transformer connections first before looking elsewhere. You can email or call Brian Smith for help. (click on "HOME" at top of Audio Note Kits Forum page)

Also you should have test speakers or 8 ohm dummy loads connected to the speaker terminals whenever the kit1 is powered up with tubes installed.
- RE: Kit1 Anode Voltage - RhythMick 02:51:37 10/05/07 (7)
  Thanks Frank. Yes I ended up checking all the way back to the mains transformer, which was putting out 467V. The diagram shows 425V. I checked the manual and it had been wired for 230V rather than 240V. I changed it and it's putting out 435V now, still higher than the diagram says, but actually you think it should be 435V anyway ?
  
  So, with the transformer now closer to where it should be and with the 900R cathode resistors back in place, I'm seeing the following ...
  
  - measured voltage coming out of the rectifier = 488V (this includes the 1.4x smoothing effect of the caps, so I think the rectifier is actually putting out 349V)
  - measured voltage drop across the cathode resistor = 74V, so I have 83mA through the valve - still too high in my view
  - measured anode voltage is 457 - MUCH better, though still above spec.
  
  Brian suggested using a dropper resistor on the output of the rectifier, say 200R. I think that will drop the measured voltage from the rectifier to around 446 but I'll have to put it in and see what happens. It will dissipate 4.5W so I'll go with 20W for safety. Once I can see the effect of that dropper I'll calculate my way through the circuit but I expect to have to change R5 and R7 to make sure that the 5687 and 6SN7 valves get the correct voltage also.
  - RE: Kit1 Anode Voltage - RhythMick 13:19:59 10/08/07 (0)
    Hi all,
    
    Just to let you know how this all got resolved.
    
    1. The transformer was rewired from 230V to 240V - made a lot of difference.
    
    2. 200R 18W dropper resister on the rectifier output, brought the 300B anode voltage down to 409V, with everything else still right. Sounded better again by a good margin.
    
    3. Cathode resistor to 1K2 20W. now at 60mA and sounding fantastic, different amp. More relaxed, but at the same time more dynamic, muscular and just bigger. Less frenetic and tiring. Significantly more bass and bass control/extension. 300B anode voltage up to 430V but inside spec. 5687 anode voltage is now 402, but happy for now.
    
    Great result all round and I highly recommend trying this. Longevity of 300B is a bonus. For interest, I used 5W Kiwame resistors (carbon film) in parallel for both the dropper and cathode resistors.
  - RE: Kit1 Anode Voltage - limono 18:07:06 10/05/07 (1)
    Hi
    You're dissipating 31.7 W in 300B tube while max is 40W.Some designers advocate running DHT's hot for best sonics. I think you're fairly safe with WE tubes.I don't think that increasing PSU impedance (chocking it) with 200 Ohm resistor is a great idea but it all depends on your listening experiments. I think most of tube manufactures allow 1o-20% tolerances on voltages. If you don't like the sound of high DCR PSU and still are concerned about WE 300b longevity your best bet is a custom power transformer
    with more current capability and electrostatic shield (mandatory like in AN finished products which helps to keep main power junk from contaminating the PSU and more important 300B DHT filament). I recommend Heyboer from Michigan
    -cool guys who do a quality job and send transformer before you make a payment.Regards
    - Also consider choke input PSU (nt) - limono 18:16:44 10/05/07 (0)
      Nt
  - RE: Kit1 Anode Voltage - Frank E 13:10:17 10/05/07 (3)
    "but actually you think it should be 435V anyway?"
    
    No, I said the B+ should be 435 VDC, on the load side of the filter choke.
    
    The mains TX should be putting out 425 Vac/rms either side of centertap, i.e. to rectifier tube.
    
    (sorry for calling the mains TX a "power TX", I hope that didn't throw you off; power TX is such a North American term)
    
    It looks like you found the problem for sure - 230V tap instead of 240. The higher voltage now is probably due to your mains voltage being a little higher than nominal. It's common for that to happen depending on how close you are to the utility HV distribution station, how many customers on your feed, time of day loading, etc. The utility runs the voltage high enough such that after line drop the customer farthest away is still in spec.
    
    "Brian suggested using a dropper resistor on the output of the rectifier"
    
    That is a good solution. Make sure the resistor is after the choke but ahead of the connection to the 220uF/450V cap. That way the resistor will filter out more of the ripple voltage and also the capacitor won't be subject to long-term overvoltage.
    
    I've used R/C (resistor/capacitor) networks for filtering and voltage drop on other amplifiers to good effect. Depending on the models and parts chosen, the sound can be much better than with L/C filters. I've found the Mills Non-inductive Wirewound Resistors to sound very nice. You could use two 12W in series or parallel to get your 20W rating. (adjust resistance values appropriately)
    
    After your voltage is optimized, you could also alter your cathode bias resistor values slightly to optimize the 300B operating point. One thing for sure, those WE 300Bs are worth taking care off.
    
    Cheers
    - RE: Kit1 Anode Voltage - RhythMick 03:19:51 10/09/07 (2)
      Thanks Frank. See my other post for a full resolution of the problem, comments welcome.
      
      The dropper resistor (200R) is on the leg of the rectifier, before the choke. It's dissipating approx 4W, so I've used 4 x 5W Kiwame carbon film in parallel. We (audio engineer friend and I) considered other solutions (removing the twin 47uF caps to make it choke-driven, droppers on the twin legs to the O/P Tx) but Brian's suggestion seemed simplest and has worked out that way.
      
      I've changed the cathode resistor to 1k2 and now have exactly 60mA on the WE300B. The rest of the circuit is in spec, the anode voltage to the 5687 is a little high, about 4% up on spec. I'll live with that for now but may change R5/R7 to drop it.
      
      The sound is WAY better. Big change once the transformer was sorted out, but another big leap getting once it was at 60mA.
      - RE: Kit1 Anode Voltage - Frank E 22:06:45 10/11/07 (1)
        
        In Reply to: RE: Kit1 Anode Voltage posted by RhythMick on October 09, 2007 at 03:19:51
        
        Good work! Glad to know that your Kit1 is now happy.
        
        60mA eh, I've never considered biasing it that low; will have to try it sometime. It might be interesting to compare the load line and distortion calcs to those at Brian's normal 75mA quiescent point.
        
        RE: Kit1 Anode Voltage - RhythMick 13:44:49 12/02/07 (0)
        
        In Reply to: RE: Kit1 Anode Voltage posted by Frank E on October 11, 2007 at 22:06:45
        
        Having heard WE 300Bs in several amps now I'm convinced that they are normally driven too hard. At 60mA they are less "in your face" and so may not be chosen in a 5-minute listening demo environment against other hard-driven amps. For an evening's listening though I find it far more enjoyable and far from losing detail, the whole system seems to produce far better micro-dynamics and tonal flavours. I'd bet they last longer too.

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