Dave's TWISTED sister - a variation of the DGSE-1 fleapower

wparks said:
So the original 8600 power transformer did not have a center tapped 6.3V filament winding- Dave G had to create a "virtual center" to the 6.3V winding with the two 100 ohm resistors that connected to the 6BQ5 cathode pin 3 to elevate the filament voltage up to cathode voltage to reduce hum.

Your Stancor PC-8405 power transformer =does= have a center tapped 6.3V winding (but I can't see the color of the lead from the one photo you have of it), so it already has a center, and in my schematic I show that center lead connecting directly to one of the cathodes of the 6AQ5, and there should be NO 100 ohm resistors.

So- Now you =can= adjust the pots? What did you set the voltage to across the 220 ohm resistor for each 6AQ5? It should be about 9.6V across each 220 ohm. This will set the correct bias current of about 48mA each tube, and the amplifier will then be properly loaded to evaluate the power supply voltage.

Since I don't know how much bias current you have flowing, 265 at the rectifier- That should be the "first cap" there, between the rectifier and the choke input. Then the 236V would be =after= the choke at the 2nd cap correct? then the 226 would be after the 820 ohm dropping resistor at the third cap correct?

Please adjust the pots for 9.6V across each of the 220 ohm resistors, report whether you can achieve that, then re-measure the power supply voltages and we can proceed.

View attachment 3721142
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So I think it will be no problem getting the 9.6 - I roughed them in at 9.5 or so
If I am hearing you I should just omit the 100 ohm resistors off the heater circuit -- Correct ?
That done do we have what is needed to do a evaluation- adjustment ?- I will double check the voltages on the filter caps and get back to you -- I think they are correct as stated though
 
Correct- omit the 100 ohm resistors from the heater circuit. But, make sure that 6.3V center tap lead is tied to one of the 6AQ5 cathodes - is that lead available, or did it get tied off?

So- if the voltage across the 220 ohms is anywhere near 9.6V (9.5V is fine) then yes- it appears there is too much voltage drop in both the 5Y3 and the choke.

Even if we eliminated the choke all together- you would still only have 265V at the rectifier- that is really too low- so there is too much drop in the 5Y3 alone. There are other rectifier options- You could go with a 5U4, a 5V4, or if you have one a 5AR4 which would be the best. What do you have?

Then the choke- you have 225 ohms through that choke, and 265-236 = 29 volts dropped across it, where with the P-T156R choke we normally use, it would be much less- like 5-7V.

So- here is what I suggest. Let us know what other rectifier tubes you have. The 5AR4 is excellent, but it's more rare and expensive. The 5U4 or 5V4 would do nicely if you have one. Try one of those, and let's see what the voltages are, =then= you may want to change the choke- but beware, the different rectifier tube and the different choke at the same time may put the voltage a bit too high- we'll have to see- so each time, dial the bias current down (lower voltage across each 220 ohm) before you try so you don't pull too much current through the tubes at the higher voltages.

5V_Rectifier_Tubes_Comparison_Chart.jpg
 
S Swanson said:
So I think it will be no problem getting the 9.6 - I roughed them in at 9.5 or so
If I am hearing you I should just omit the 100 ohm resistors off the heater circuit -- Correct ?
That done do we have what is needed to do a evaluation- adjustment ?- I will double check the voltages on the filter caps and get back to you -- I think they are correct as stated though
Click to expand...
I did the measurements again and they are -- after i adjusted the bias -266 pin 8 of the rectifier -235 1 st filter After the choke and 221 after the 820 resistor
 
S Swanson said:
So I think it will be no problem getting the 9.6 - I roughed them in at 9.5 or so
If I am hearing you I should just omit the 100 ohm resistors off the heater circuit -- Correct ?
That done do we have what is needed to do a evaluation- adjustment ?- I will double check the voltages on the filter caps and get back to you -- I think they are correct as stated though
Click to expand...
I did the measurements again and they are -- after i adjusted the bias -266 pin 8 of the rectifier -235 1 st filter After the choke and 221 after the 820 resistor
 
Ohh yes! Plug in a 5AR4, re-adjust the voltage across the 220 ohms to 9.6V for each side, and report back what the voltages are!
 
Is that with all the tubes in, and bias set to correct currents? Please give the voltages.

Or maybe try a different 5Y3 if it really makes that much difference. Maybe the first one was worn out?

Please give me info or I cannot help . . .
 
wparks said:
Ohh yes! Plug in a 5AR4, re-adjust the voltage across the 220 ohms to 9.6V for each side, and report back what the voltages are!
Click to expand...
I could not get the 9.6 on the TPs perhaps with some of the other tubes - perhaps - I did get one tube to 10v and checked for the filter caps voltages all were over 300v - I suppose I could fiddle with the other 6aq5s to see if i can bring down the voltage in the bias
A note here when I found that the 5y3 ( the original had failed ) I replaced it with a 5y3 GT -
And there is a voltage drop difference of about 16 v to the original - still seems to little compared to the 5v4-g
 
Ok, now with the better 5Y3, set the bias current, and please give me all of the voltages. The problem was clearly a bad 5Y3.
 
wparks said:
Is that with all the tubes in, and bias set to correct currents? Please give the voltages.

Or maybe try a different 5Y3 if it really makes that much difference. Maybe the first one was worn out?

Please give me info or I cannot help . . .
Click to expand...
Understood - Had to go out -- I noted from the chart that the Plain jane 5y3 had less voltage drop than the 5y3 gt - I do have another 2 examples of the 5ar4 , and a example of 5y3 GT --- but at a 60 v drop ,I cant see how that is going to help - and quite a few 6AQ5s that may make a difference - Further as I am thinking of using the 5ar4 ---I don't have - quite enough resistance --correct --- I could add something there
 
5Y3G and 5Y3GT are the same tube in a different bottle. Same voltage drop within the tolerances you'd get tube to tube. If one is tired, it will drop more voltage.
 
S Swanson said:
Understood - Had to go out -- I noted from the chart that the Plain jane 5y3 had less voltage drop than the 5y3 gt - I do have another 2 examples of the 5ar4 , and a example of 5y3 GT --- but at a 60 v drop ,I cant see how that is going to help - and quite a few 6AQ5s that may make a difference - Further as I am thinking of using the 5ar4 ---I don't have - quite enough resistance --correct --- I could add something there
Click to expand...
so with the 5ar4 at pin 8 its 337.5 1st filter cap @312.5 and after the 820 resistor 304 or so == not warmed up though, and I could not bring the voltage down enough on the test points - one was 10 the other 11 and change
 
You are all over the place, not getting voltages, not doing this step by step and giving information to analyze and direct the next step, so it is very frustrating.
Slow down, and lets do this step by step, and don't jump over the process.

@gadget73 is right, if the first 5Y3 was worn out, the new 5Y3 will give higher voltages. (Didn't I say that earlier?)

All voltages should be collected with the amp warmed up for a minute, and =all bias currents set for 9.6V across the 220 ohm resistors=

PLEASE GIVE ME: new 5Y3, bias currents dialed in, and voltages . . .
 
S Swanson said:
OK not a big deal to try the other -
Click to expand...
Results are closer -- with the new (to me) 5y3gt Pin 8 on the rectifier stands at 295v and the first filter-cap after the choke is 268v and after the 820 res it is 262v not warmed up much though
still Can't quite get to 9.6 one got there the other maxed out at 9.8
 
Ok, GREAT! I can work with this.

Voltage after the choke is 268V, which is a great voltage for the plate- this will likely put the plate in the ball park of 250-260, which is fine. I suspect that the reason you can't get both 6AQ5 tubes down to the bias current we want is because the screen voltage is running a bit high at 262V. I'd like to see what you get with the screen voltage closer to about 250V, and to do that, try changing the 820 ohm to more like 2K ohms at 1W. If you can't do that, throw a 1K 1W in series with the 820, and try again, and get the new voltages.


S_Swanson_6AQ5_DGSE-1_Sketch.jpg
 
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