what gs5556 said.
1V/15k ohms = .00007 amps = .07mA = teensy weensy
Voltage regulators and input impedance
I have an Audio Research Ref 5SE pre running into a Modwright KWA 100SE power amp. The input impedance of the Modwright is listed as “15K at 50 Hz” and the specs on the Ref 5 suggest “20K ohms minimum load”.
So here is my question: I have gone through 3 6550 tubes in the Ref 5 (which AR says is used as a “voltage regulator” in the power supply) in the past 3 years - sovtek, tung sol, svetlana, all new. The last one lasted under 500 hours. I am thinking of potential causes, including excessive heat (the location needs better ventilation), something wrong with the preamp, etc, but I am wondering about that input impedance on the power amp. Am I running the Ref 5 into too little of a load? Would that put undue strain on the power supply tube, causing it to fail prematurely? Would love to hear from someone who knows this stuff better than I…
- ...
- 14 posts total
I just want to correct what I wrote on 06-01. I guesstimated the output impedance of the PH5SE at 200 ohms, based on the recommendation to mate it with an amplifier of not less than 20K ohms input Z. In fact, if one applies the 1:10 rule of thumb, I should have guessed the output Z at 2000 ohms, not 200 ohms. In fact, ARC say its output Z is 300 ohms unbalanced/600 ohms balanced. Mea culpa. But in view of the facts, I wonder why ARC recommend to drive an amp with not less than 20K ohms input Z. In theory, the PH5SE could work just fine with an input Z much lower than 20K ohms. Could be that the output Z of the PH5SE rises at frequencies other than 1 kHz, where the measurement is usually done. Also, input capacitance presents an impedance that is in parallel with the resistance. This can cause a high frequency roll-off if the input/output impedance ratio is not a healthy greater than 1:10 ratio. Anyway, the main point is that the matching of the two components is almost certainly not causing the 6550s in the ARC PS to blow or wear out prematurely. |
@itsjustme - That was me actually. 😁 |
- 14 posts total