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Questions on 6H30 simple PF?

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pengboon

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Joined 2005
I have made a simple single stage plate follower using a 6H30pi (Sovtek). It is partnered to a SS power amp (about 19k i/p resistance), and I am running at about 90V, 12mA. I had solved the hum and buzz problems with filters in the power supply circuit. Tried >20mA but I thought the lower current sounded more relaxed. Are there any more variations/brands of this tube I could try, and what are the effects? I know (from this great board that there are better circuits and tubes out there, but I just want to make this one work as best I can for now...)

I also find the gain to be very high, as in I never have to turn more than a little of the vol pot. Anyway, I am wondering if I should lower the gain, and how should I go about it? I am not using a cathode bypass cap. Or just live with just using 10% of the vol pot? Plate resistance is 10k (after B+), cathode resistance is 180, grid stopper is 1k. Output coupling cap is 1uf with 100k resistor.

any advice is appreciated as I am still very new to this (1st timer), thanks for any assistance... ! :)
 
TonyTecson

TonyTecson

Member
Joined 2003
selamat malam,

you can increase the cathode resistor to say 330 or 470ohms and work your way from there, you can also decrease plate resistor from 10k to say 8.2k.

btw, are these tubes easliy obtainable in singapore? sim lim square? and for how much? i worked in singapore from 1997 to 2001. at jurong island.

tony
 
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pengboon

Member
Joined 2005
Thanks Tony, I guess I will have to experiment on it? Is there any way to calculate (or at least get a good estimate) on the gain?

I'm also toying with the idea of changing my output coupling cap, currently, it's a Solen 0.33uf. Thinking of swapping to a Jensen or Mundorf S/O, any comments about these? What's the likely effect of either? Actually, I'm pretty happy with the preamp now (it simply trashes my previous SS though I'm still using a SS Yamaha poweramp), just thinking (as always) of how much better it can get with some component(s) upgrade.

Another question, for grid stoppers, plate and cathode resistors, do I need to invest in real good quality ones?

thanks again!
 
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pengboon

Member
Joined 2005
Operating Point?

I have tried to set the 6H30pi at 2 different operating points:
1) Va=93V, Ia=23.8mA, Ra=4.55k, B+=205
2) Va=68V, Ia=16.4mA, Ra=10k, B+=232

The change from 1 to 2 was done by changing the Ra only. I found point 2 more "relaxed" Both sound just as detailed and clear to me. What should I be looking out for as both points seem pretty linear to me...

Any advice on other operating points to try out? I read that 120V, 20mA is good, am I able to get there without changing the power supply circuitry, it seems not possible in the current setup?
 
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