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 on: September 30, 2022, 09:59:34 AM 
Started by KL7OF - Last post by WA1QHQ
Most of what I see that matches your description is ionosphere sounders that are used to determine the MUF of a band at any given time, often used by the military. I live a few miles from where the "Boston Buzzy" emanates from so I hear those sounders alot.

 on: September 29, 2022, 08:38:32 PM 
Started by af6im - Last post by af6im
Got a nice Desk KW complete, appears all original, but hasn’t operated in over 20 years. Reportedly working ok when retired. Any suggestions on where to start, what to test and known pitfalls for Desk KW newbies? Any assistance greatly appreciated.


 on: September 29, 2022, 12:21:25 PM 
Started by w4pjp - Last post by w4pjp
Thanks for all the comments! I hope others will chime in, this topic is not discussed much anywhere…..

John, good to see u at the hamfest….didnt know you were interested in AM!


 on: September 29, 2022, 10:47:35 AM 
Started by w4pjp - Last post by KD6VXI
I ran my sb220 on the ssb switch constantly.

The only time it saw the cw switch was at turn on.  It lowered the in rush current.

I always like aded it to the pep value I needed for the carrier level.

Caveat:  I don't do digital modes, including CW 😉


 on: September 29, 2022, 10:40:51 AM 
Started by pe1mph - Last post by pe1mph
Hello AM Lovers,
I was in my studio to sent some emails.
My old Yaesu FT 901 DM standing on 21.420 in AM.

Nearly I fall from my chair....
I heard K1GUP calling in AM!
And I were wondering how good I hear him.
So I give him a call back....

We had a short and nice talk in AM on 21.420 khz.
He by me: S2 - 5 and R 5!

While I type this, I hear him talking with another station...
But no idea who, because I hear only K1GUP.

After our talk Jerry I heard another station from the USA calling?
But I could not copy his call or name....


Henk / pe1mph
Dokkum / The Netherlands

 on: September 29, 2022, 09:26:30 AM 
Started by lu8dam - Last post by lu8dam
Best of all, it seems that this insignificance does not cause any effect, and yet it does.
That is what always encourages me to experiment.

 on: September 29, 2022, 08:38:14 AM 
Started by lu8dam - Last post by KA3EKH
The next question would be do different oils have different acoustic properties? What sounds better? Castor or Silicon? Is Castor best for Classical and Silicon best for modern music?  Don’t know if it has been used yet but maybe something like e thin grade motor oil for Country?
In theory you can install a small drain plug and filler top and have different oils for establishing a mood.

 on: September 29, 2022, 01:15:21 AM 
Started by lu8dam - Last post by Opcom
An audioplile sort of tube amp builder used to appear at the old surplus store and buy up all the small-value, old metal cased oil caps. He swore there was a big difference in listening when using them for interstage coupling and general decoupling, even to the point of putting a 1uF across an electrolytic filter. He got all the little 0.1 to 1uF ranges of 'bathtub' oil caps. He said the same that he could hear the difference. he also said that the oil caps were better because the innards didn't vibrate.

I can only attest that I have heard some old tubular coupling capacitors 'sing' when audio voltage was placed across them, denoting I suppose the vibration.

 on: September 28, 2022, 10:42:08 PM 
Started by lu8dam - Last post by W7TFO
I use a lot of Sprague "Vitamin Q" oil caps in my audio builds.

A lot of the Russki KY- types as well, then they got expensive. Tongue

Both are PIO as far as I know.

Both are good at audio tasks.

Nothing wrong with poly caps, I use them in receiver recapping.

73 Dennis

 on: September 28, 2022, 10:38:46 PM 
Started by N3GTE - Last post by DMOD
Here is a circuit that I use that retains the 12BY7A:

It takes the DC off the driver transformer so as to prevent saturation of the driver's core.

Phil -- AC0OB

Phil, skip those back to back electrolytics!
Use a nice Mylar or Polypropylene cap. Looks like you call for ~10ufd, these are easy to
find in over 400volt ratings...

Since ur driving  7k ohm primary, do you actually need or want 10ufd?
A queeck calculation says that 10ufd and a 7kohm load gets a -3dB frequency of
 2.2747952684 Hz!
So 1 ufd will get 22.27479...Hz.
Which, imho is still to low, given the inherent core limitations of the mod iron!
Something between that 1ufd, and ~0.5ufd would in theory put the -3dB around
30-40Hz, which is pretty darn good.(if it works as the calculation holds, then 0.6ufd will get
38Hz as the -3dB point, which BTW will still have a fair amount of energy an octave below!)
 And, will help avoid inadvertently swamping the mod iron.

Not to mention that the driver iron isn't going down to 2Hz or 20Hz... fwiw.

Testing in practice to find the actual -3DB point is a good plan.
For easy testing, half voltage is 6dB down.

it sounds as if you modeled it as a high impedance, RC coupled circuit.

I modeled it as a low impedance series resonant circuit, with a primary inductance of 6.4H, which gives us a low frequency starting point.

Phil - AC0OB

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