I was curious about actual current flow through R1 under your operating conditions, as well as the heat generated. Measure the DC voltage (Vr1) across R1 under quiescent conditions. You know R1=122 Ohms. Calculate Ir1 = Vr1 / 122 amps; and R1 dissipation (Pr1) = Vr1 * Ir1 watts.
Edit: @jcalvarez was quicker than I
Edit: @jcalvarez was quicker than I
I'm trying to win "calpe's best supporter" trophyEdit: @jcalvarez was quicker than I
There i was tapping my feet, but not to some funky Rhythm & Blues, but at some jack **** who delivered my A.C. fan to the wrong person at the wrong address. My thoughts were distracted, and I got completely fed up of the situation and turned my back on the Tube Lab build. After so much hassle 4 weeks later i was finally refunded! This is the wonderful Chinese version of Amazon, called AliExpress.
The seller resent another fan, arriving a few days ago.
Apart from this all public holidays are now over (apart from one in June), so I’ve decided to kick myself to get things finished.
If I may (with the readers support), I would like to go a few points to make absolutely sure things are as they should be.
Just to note that where R1 (150R 5W) originally was there is now a 1.5H 200mA choke.
As we know my H.T. was way too high, so a 122R 5W is connected between the main secondary’s centre-tap and ground. This brought the H.T. down to 320V.
I will check this again over the next few days.
My main concern is to make sure the Valves are biased correctly.
Could you please tell me again the measurements I need to do and also the calculations?
Again, i pass on my warmest thanks to you all.
The seller resent another fan, arriving a few days ago.
Apart from this all public holidays are now over (apart from one in June), so I’ve decided to kick myself to get things finished.
If I may (with the readers support), I would like to go a few points to make absolutely sure things are as they should be.
Just to note that where R1 (150R 5W) originally was there is now a 1.5H 200mA choke.
As we know my H.T. was way too high, so a 122R 5W is connected between the main secondary’s centre-tap and ground. This brought the H.T. down to 320V.
I will check this again over the next few days.
My main concern is to make sure the Valves are biased correctly.
Could you please tell me again the measurements I need to do and also the calculations?
Again, i pass on my warmest thanks to you all.
Attachments
Glad you can move forward now. I hope your fan will be quiet enough.
Since the stock SPP is a cathode bias design you cannot adjust the bias per se. If you wanted to check your operating point you can re-measure the data points in #505 quoted above. Then calculate the cathode current by I=V/R (this is the combined plate and screen current), and recheck the plate dissipation, for example:
For V101 -
V (cathode) =10.6V and R=300, so
Vcathode =10.6/300 = .0353, i.e. approximately 35 ma.
Combined plate and screen dissipation then is:
V (across the tube) = 315-10.6 = 304.4 V
Dissipation = V*I = 304.4 * .035 = 10.65 watts
These numbers are quite conservative and your tubes should happily live a long time if these measurements above are still valid for your SPP.
I am a bit nonplussed at the location of that resistor, from the CT to ground? I was trying to see who suggested that but after wading through a few pages I was none the wiser. Doesn't it see a lot of ripple where it is put? And won't it play havoc with the B+ when the tubes draw more current? Doesn't it impact the resistance divider for the HK cathode protection (20 volts less)?
The mistake here was the choke does not have the 150R resistance that is specified in the Tubelab SPP build guide, In which case I would firstly have replaced the choke with the 150R that you have so it is built as specified. Then Plan B would have been to add another capacitor, and put the resistor after the choke and have a CLCRC supply instead.
The mistake here was the choke does not have the 150R resistance that is specified in the Tubelab SPP build guide, In which case I would firstly have replaced the choke with the 150R that you have so it is built as specified. Then Plan B would have been to add another capacitor, and put the resistor after the choke and have a CLCRC supply instead.
The discussion started at around post #441 when I concluded the resistances of the Primary Windings power transformer’s (PT) secondary windings were too low to use with an unprotected 5AR4, and suggested a 100 Ohm resistor in each lead between the transformer and 5AR4 anode. You agreed.
@6A3sUMMER, starting in post #456, suggested that a “shared” 50 Ohm resistor between the PT center tap and ground would be equivalent. I was persuaded and I thought you were too, at least tacitly. Think it over and we could discuss further. But I believe it will work fine and not wreak havoc with anything.
@calpe had a combined resistance of 122 ohm available that he tried in the center tap lead and liked the results. His build proceeded from there with the somewhat lower than specified B+ of 315v DC, but I believe he preferred the slightly lower power and dissipation, with the added safety and tube life, compared to maximizing power and reducing tube life.
@6A3sUMMER, starting in post #456, suggested that a “shared” 50 Ohm resistor between the PT center tap and ground would be equivalent. I was persuaded and I thought you were too, at least tacitly. Think it over and we could discuss further. But I believe it will work fine and not wreak havoc with anything.
@calpe had a combined resistance of 122 ohm available that he tried in the center tap lead and liked the results. His build proceeded from there with the somewhat lower than specified B+ of 315v DC, but I believe he preferred the slightly lower power and dissipation, with the added safety and tube life, compared to maximizing power and reducing tube life.
Even my correction in Post # 462 may have been wrong.
Instead, use 100 Ohms, 10 Watt in the center tap lead.
That gives you 100 Ohms, when either plate conducts.
If that does not drop enough voltage, use a 150 Ohm 10W resistor, etc. as necessary.
One resistor is easier to place in the chassis than Two resistors, but be sure to leave lots of air around the single resistor.
Instead, use 100 Ohms, 10 Watt in the center tap lead.
That gives you 100 Ohms, when either plate conducts.
If that does not drop enough voltage, use a 150 Ohm 10W resistor, etc. as necessary.
One resistor is easier to place in the chassis than Two resistors, but be sure to leave lots of air around the single resistor.
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Good evening all, and again may i thank you all for your interest and professional inputs.
Facts: -
B+ should be between 320-340V
Primary Winding U.K. Mains Tx secondary winding = 72.5R
Primary Winding U.K. 1.5H 200mA Choke = 15.4R
CL-80 fitted.
Rather than reply to each post, i'll make some comments below.
#532 - I chose a very quiet fan (might be removed). Voltages checked today are below.
#533 - The Valves were purchased as matched pairs from Watford Valves U.K.
#534 - Check out post #467, second paragraph - 'more resistance between the secondary C.T. and ground'. I worked with several values and settled for 122R, it lowered the B+ to what i need. Will it cause problems?
Question is do i remove it and add in series resistors between the secondary windings and the Cathodes of the 5AR4? Values to try would begin at 100R 3W.
#447 - Indeed it should try removing the choke and install the original design of R1=150 5W. If there is any hum i'll reinstall the 1.5H choke.
#467 - Says 'the dissipation in R1, i noticed that its dissipation is rather high, so we may need a bigger resistor here for the final one. Perhaps a 7 or 10 watt? With the 122R i have fitted, they do run warm, so i'll probably up the wattage.
Voltage measurements: -
B+ = 316v
Cathode V102 = 10.86v
Cathode V101 = 10.64v
Cathode V202 = 10.67v
Cathode V201 = 10.95v
R113/V101 pin 9 = 312.5v
R117/V102 pin 9 = 312.7v
R213/V202 pin 9 = 312.4v
R217/V201 pin 9 = 312.5v
Facts: -
B+ should be between 320-340V
Primary Winding U.K. Mains Tx secondary winding = 72.5R
Primary Winding U.K. 1.5H 200mA Choke = 15.4R
CL-80 fitted.
Rather than reply to each post, i'll make some comments below.
#532 - I chose a very quiet fan (might be removed). Voltages checked today are below.
#533 - The Valves were purchased as matched pairs from Watford Valves U.K.
#534 - Check out post #467, second paragraph - 'more resistance between the secondary C.T. and ground'. I worked with several values and settled for 122R, it lowered the B+ to what i need. Will it cause problems?
Question is do i remove it and add in series resistors between the secondary windings and the Cathodes of the 5AR4? Values to try would begin at 100R 3W.
#447 - Indeed it should try removing the choke and install the original design of R1=150 5W. If there is any hum i'll reinstall the 1.5H choke.
#467 - Says 'the dissipation in R1, i noticed that its dissipation is rather high, so we may need a bigger resistor here for the final one. Perhaps a 7 or 10 watt? With the 122R i have fitted, they do run warm, so i'll probably up the wattage.
Voltage measurements: -
B+ = 316v
Cathode V102 = 10.86v
Cathode V101 = 10.64v
Cathode V202 = 10.67v
Cathode V201 = 10.95v
R113/V101 pin 9 = 312.5v
R117/V102 pin 9 = 312.7v
R213/V202 pin 9 = 312.4v
R217/V201 pin 9 = 312.5v
Francois G,
As you know, the dissipation of the 122 Ohm resistor is very complex.
Look at it this way, the dissipation is the integral of V-squared/R; R= 122 Ohms
Set the scope for Cycle RMS, and then square the voltage measurement value, and divide by 122 Ohms.
If the scope can not "decide" what is a cycle, then set the scope time to show several alternations, and set the measurement to full time scale RMS.
You will get at least two different answers, under the following conditions:
1. Quiescent dissipation, and Class A push pull dissipation are relatively the same. (so is single ended class A)
2. Large signal Class AB push pull dissipation is greater.
Have fun measuring!
As you know, the dissipation of the 122 Ohm resistor is very complex.
Look at it this way, the dissipation is the integral of V-squared/R; R= 122 Ohms
Set the scope for Cycle RMS, and then square the voltage measurement value, and divide by 122 Ohms.
If the scope can not "decide" what is a cycle, then set the scope time to show several alternations, and set the measurement to full time scale RMS.
You will get at least two different answers, under the following conditions:
1. Quiescent dissipation, and Class A push pull dissipation are relatively the same. (so is single ended class A)
2. Large signal Class AB push pull dissipation is greater.
Have fun measuring!