Help w/ diyAudio CCS implementation

[arnoldc]

Hi guys, I grafted my diyAudio CCS board to my 300B amp. I replaced the 10K plate resistor with the CCS board (HV PNP CCS) set for 10mA. The cathode bias for the 417A is still an Orange LED.

R1 is set to 22K for ~7mA to fire up the LED.

R2 is set to 100R for 10mA current (1V/10mA), R3 is jumpered.

Transistors are 2N3906 and MJE 350.

417A plate voltage is 127V, from B+ of 143V. Cathode voltage is 1.9V (same as before)

The problem:

I'm getting distorted sound and overloading (cathode LED flashes wildly when signal is fed to the amp)

Where did I go wrong?

[Katapum]

Hi,

Originally posted by EC8010
I like to be able to swing double the expected swing. You need to swing 45V positive, so 90V of capability would be nice. I suggested 120V because that's probably the amount you need to drop from the HT to your anode voltage, and yes, you need a bit of a margin for the CCS.

Katapum

[ErikdeBest]

417A plate voltage is 127V, from B+ of 143V. Cathode voltage is 1.9V (same as before)

Katapum already gave the answer. The 417 plate van swing to a maximum of 143 volts (the B+), well, not even that because there is some loss in the CCS (dropout). So with this stage you can swing a maximum of 20V peak to peak, without clipping.

That's some theory I have started to understand in the last months. Don't know if it is right, if it's wrong I am sure others will correct me!

Erik

[tubelab.com]

That's some theory I have started to understand in the last months. Don't know if it is right, if it's wrong I am sure others will correct me!

You are quite correct. You need at least 100 volts P-P to drive a 300B, and possibly as much as 150 volts. My 5842 - 300B amp uses 375 volts as the plate supply for the CCS that feeds the 5842. I use the same supply that feeds the 300B. The PSRR of the CCS lets you get away with this.

[arnoldc]

Thanks for all the replies.

I realized it will not be as forgiving as a simple 10K plate load I was eyeing around 150V but thought that 127V is still close to the textbook voltage of 130V (but at 20 something mA). Anyway, my fault.

tubelab, my B+ is 390V and I'm really tempted to be brave as you but isn't it that the max plate voltage of the 5842 is 200V?

The CCS drops just 16V and I will be waaaay over 200V max.

[Zen Mod]

Originally posted by arnoldc
Thanks for all the replies.

I realized it will not be as forgiving as a simple 10K plate load I was eyeing around 150V but thought that 127V is still close to the textbook voltage of 130V (but at 20 something mA). Anyway, my fault.

tubelab, my B+ is 390V and I'm really tempted to be brave as you but isn't it that the max plate voltage of the 5842 is 200V?

The CCS drops just 16V and I will be waaaay over 200V max.

orange LED is what really dictates A to C voltage in your circuit (look at tube as on variable resistor,where resistance is dictated with Orange LED - talking in terms of steady state ) ;

you can crank Ub to zillion volts,under condition that your CCS will withstand this voltage-where voltage is in fact difference between Ub and Ua-c ............

I will not dispute Tubelab's bravery,but in this case he 's not brave, just (or JUST) practical

[arnoldc]

Hi choky, I did take that into consideration when working out on a B+ voltage. Vk=2V + Va=130V = 132V (which I still miss by 5V)

I guess I had a misinterpretation with a CCS in the circuit vis a vis plate load. It seems to be that I will see a horizontal load line instead of the normal angled one with a CCS.

So I'll bump this up and go for 200V Va - 2V Vk = 198V. If I take it direct from B+ of 390V that will be 192V so I just have to worry if the transistors in the CCS can take this?

edit:

On second thought, maybe I should just crank up B+ supply to CCS with reasonable dissipation on the parts.

[Zen Mod]

hehe-=do not be so peeky with voltages ......except when you think about cathode bias voltage;everything else can be certainly in range of +/- 10% and you'll hardly hear the difference....


what I meant- biasing element,in your case Orange Led , will take care about voltage between cathode and anode of tube ...in your case ~ 130V ,if I understood correctly.... ;
so -if you have bias voltage in range of 2V , CCS will burn every excessive and unneeded volt ...no matter if your high voltage supply gives you 200 or 400V........
but-more is better,so just put decent heatsink on MJE and crank it full throttle !

[arnoldc]

gotcha!

Thanks again choky!

ps.

That made my life a lot easier because this amp takes in 10Y/50/300B tubes and now I don't have to worry about voltage variations for the driver stage

Amp porn added:

[Zen Mod]

Originally posted by arnoldc
gotcha!

Thanks again choky!




Amp porn added:

now you can send to me all your 10Y/50/300B un-needed toobz for proper disposal