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 on: Yesterday at 11:17:50 AM 
Started by wa2tak - Last post by Opcom
Several vintage tube type 0-400V commercial bench supplies here which are floating in all respects, B+, filament, bias, whatever they supply. They have chassis-grounding power cords. Have put two in series for up to 800V many times. Agree on the remark about less than 1000V total.

I would not necessarily do it with solid state units, who knows what can happen if one fails it could take the other one with it because of issues with the load and transients.

 on: Yesterday at 11:06:55 AM 
Started by wa2tak - Last post by Opcom
Other than checking to see if it will stand the plate voltage to be used, not much, as you must have filament power.

Can you find an old style 'analog' car battery charger of more than 4 Amps?
It will have a transformer of anywhere from around 6 to 24 volts depending on whether it's a 6V or 12V unit, and if it has a full wave center tapped or bridge rectifier. Can you use a variac on the primary to adjust the secondary voltage to 6.3V?

 on: Yesterday at 08:46:11 AM 
Started by wa2tak - Last post by wa2tak
Picked up a vintage home brew 2 x 811A amp.
One had broken glass at the plate cap.

Would like to know if the other is OK.

The heater needs 4 amps...my PS does not go that high.

What to do, please?

 on: May 27, 2023, 02:56:42 PM 
Started by KL7OF - Last post by KL7OF
I saw this on another site.   KA2CAF  has free for pickup BC1G, BC1T, BC1H, GATES    BTA500, BT1R1.  RCA...Hope someone can save these.   Steve

 on: May 26, 2023, 04:18:54 PM 
Started by SA2CLC - Last post by SA2CLC
I'm currently using an HP8640 as vfo, while building an ESP32-si5351a dedicated vfo.
The 8640 appears to have enough drive, although I have not verified that there is at least 8v pk-pk on the grid of the mixer.
I say appears, because I can "peak" the transmitter output using the generator; if I increase the generator output above a certain level, the power out from the transmitter decreases.
The reason I'm looking for those last watts is because they are needed to drive the dual grid driven 813 linear. Right now it falls a bit short.

Checking output power using a crystal (only got a 40m) yields about the same power as with vfo, about 12w.

I did swap the cathode follower driver, a 12BH7, which increased the output power on 10m from 1.5w to almost 8w, which I'm quite pleased with, however,  no improvement on the lower bands.

A NOS (yeah right!) 6BA7 mixer off Epay gave less power than the one that was in the transmitter. (That tube tester build should have gotten priority over new projects!!).

I guess I should start measuring pin voltages before anything else. I did replace all capacitors, sans micas, but there are still possible drifted resistors in the mess.

 on: May 26, 2023, 02:56:20 PM 
Started by wa2tak - Last post by KD6VXI
I have a Peter Dahl 6A 3 kv ac out xformer.  That gives 4.2kv at 6A CCS on a customers 2 x 3cx3000A.

He was slightly low on pep drive so I said the easiest fix is to uo the gain by upping the voltage.

Control xformer, 120/208-240 to 480.  480 is hitting a doubler giving a bit over 1.3kv.

Together, at 5kv under load, it hit the spot. Hes happy.  Been in operation for 3 years.

I don't know that I'd try it with commercial supplies until I had opened them up and verified that the - lead was utterly isolated from the chassis.


 on: May 26, 2023, 10:57:53 AM 
Started by K4NYW - Last post by WBear2GCR
As usual Nick, great browsing with you.

The guy with the 20 Rangers, and 30 Hammarlund HX-170s??

Saved me a lot of driving, and money to just look at ur pix!!
A few items I would have like to come away with - but...


 on: May 26, 2023, 10:55:05 AM 
Started by WBear2GCR - Last post by WBear2GCR
Not generally appreciated, but both CFLs and LED bulbs when looked at with a spectrum analyzer put out
strictly 3 monochrome colors: red, green, and blue!!

That's due to the use of rare earth phosphors.

(which if they were so darn expensive and difficult to get, you would think they would recycle??)

Whereas incandescent bulbs are actually "full spectrum" to the extent that there are no individual bands of colors.

Which in part is why these modern bulbs "don't look quite right"!!


 on: May 26, 2023, 10:49:38 AM 
Started by wa2tak - Last post by WBear2GCR
One needs to be quite careful when doing this with voltages above say 50 volts!!

IF the upper PS has its negative lead connected to the positive lead of the lower supply,
the center point is now at the upper supply's voltage. 400volts in your example.

IF the negative terminal of the upper supply is connected to the CHASSIS,
and that power supply has a two wire plug, and therefore is not grounded to the
AC MAINS "safety ground" (the "third pin") THEN the chassis (the box) that you will
touch will be AT 400 volts!!

No good.

So, the supply actually floats (and those supplies typically have 3 binding posts for outputs, negative, GROUND, and positive) you are okay...


PS. in the case of building such a supply inside a chassis, for a piece of homebrew gear, not a problem.

 on: May 26, 2023, 10:43:46 AM 
Started by wa2tak - Last post by WBear2GCR
Well, it's not really covered in the texts... but in fact it is all magic!!

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