Push Pull Powersupply Test Question?

[DualTriode]

Hello,
This is today’s test.

The goal is old a old school 1625 (807) Push Pull amplifier, before firing up an unknown powersupply into the final tubes I want to use I am plugging in a pair of 6P3S’s (close to 6L6**’s). The power supply is a 272HX Hammond 300-0-300 220ma, Russian 5AR4, 47uf (measures 44uf) capacitor, 6Hy Triad 200ma choke and 600uf of capacitors. The goal is about 140ma at 375 DC volts. The input AC voltage is ~ 122.
By the way there are two 6sn7’s (6H8C’s) also firing up in the test.

I will post the results!
Any guesstimates as to DV volts near 140ma output?
I know good luck.

DT
All just for fun!

[DualTriode]

Hello,
This is today’s test results.
Note the 272HX has 115 and 125 volt taps on the primary the test was done on the 115 volt tap.
The AC voltage at the wall outlet was 123.
The AC voltage at the heaters was 7.14.
The DC voltage at the input of the choke was 403. 28 volts higher than the goal.
The DC voltage at the output of the choke was 379.

My guess is that the 125 volt tap will give 370 volts B+ at the input of the choke and reduce the AC voltage at the heaters. That is tomorrow’s test question.

DT
All just for fun!

[VictoriaGuy]

Originally Posted by DualTriode

The DC voltage at the input of the choke was 403. 28 volts higher than the goal.

I thought you were aiming for a B+ (ie choke output) of 375vDC?
My guess is that you will get about 350v B+ with the 125v primary tap.

Tweak, tweak...fun, huh?

[DualTriode]

Originally Posted by VictoriaGuy

I thought you were aiming for a B+ (ie choke output) of 375vDC?
My guess is that you will get about 350v B+ with the 125v primary tap.

Tweak, tweak...fun, huh?

Hello VictoriaGuy,
You are correct, after the choke is the place to test B+ voltage.
This morning the wall AC is a couple of volts lower at 121. Before the choke the voltage is 367 after the choke the voltage is 346, you get the prize.

The data sheet for the 5AR4 says the maximum value capacitor before the choke is 60uf. The installed capacitor is labeled 47uf and tests at 44uf. I bought 20 expecting +- 20% but no they were all the same within a couple of grey whiskers. perhaps the addition of 5 or 10 uf will increase the B+ a few volts?

I am going to try several versions of voltage splitters before the finished product; Long Tailed Pair, …..this effort on the breadboard is Pete Millett’s Uniamplifier/Driver with a transformer doing the splitting for Push Pull. Pete’s schematic shows B+ before the choke and that is where he measured the B+ voltage. Where the B+ voltage meets the road is between the Plate and Cathode.
Push-pull KT88 class A amp with "universal" driver PCB

There is also Edcor 25 watt 7.6K : 8R transformer and a 100R resistor installed between the choke output and the Plate.

Yes Fun!

DT
All just for fun!

[VictoriaGuy]

Originally Posted by DualTriode

The data sheet for the 5AR4 says the maximum value capacitor before the choke is 60uf. The installed capacitor is labeled 47uf and tests at 44uf. Perhaps the addition of 5 or 10 uf will increase the B+ a few volts?

I don't think that will make much difference. I use Duncan Amps PSUD for this sort of tweaking (on 'paper') and it's really useful. Give it a try...

Anyway, not a big deal to be 'dead on' the B+, IMO. You might need to change some resistor values to make sure the tubes are running 'hot' enough to compensate.

[VictoriaGuy]

Originally Posted by DualTriode

…..this effort on the breadboard is Pete Millett’s Uniamplifier/Driver with a transformer doing the splitting for Push Pull.

Did you have something in the parts box for input transformers? The ones Pete Millett mentions are a bit pricey for me. 45GBP ea..

Should be a nice project.

[DualTriode]

Originally Posted by VictoriaGuy

Did you have something in the parts box for input transformers? The ones Pete Millett mentions are a bit pricey for me. 45GBP ea..

Should be a nice project.

Hello VictoriaGuy,
Both of the input transformers Pete has setup look to be high end products. I bought a pair of the Lundahl LL1690’s I also bought a pair of pair of Edcor matching transformers in a box EDCOR Electronics Corporation. S2S10Kt/10Kt . The Edcor transformers were $28 for both in the box as you see on their site. I plan on trying several versions point to point on the PCB’s to see how things work out prior to locking the Lundahl’s to the PCB forever. I also plan on trying out the Williamson amplifier approach. I will slide the breadboard into an Old Gary Box and let it run for awhile to see how I like in its various forms.

DT
All just for fun!

[VictoriaGuy]

The Edcor looks more in my league.

Do you have a thread going about your amp build (other than this one) ?

[costis_n]

Better use the 125V primary configuration, heater voltage is too high!

[VictoriaGuy]

Originally Posted by costis_n

Better use the 125V primary configuration, heater voltage is too high!

+1