Restoring a small transmitter

AM Radio discussion. Directional arrays are FUN!
Patrick De Landsheer
Posts: 7
Joined: Thu Nov 27, 2014 3:21 pm

Re: Restoring a small transmitter

Post by Patrick De Landsheer » Mon Apr 25, 2016 12:16 pm

I m sorry to have taken so much time to reply. The small transmitters and the linear amplifiers were modify and custom made by Mr Cunningham for a friend who gave them to me. I will look for the brand of those amps. They are Ham radio amps and the power is 400 watts no 2000. A friend provide me with 1mhz crystals. As I said before, I need to change frequencies. From 1620 ot 1610 khz to 1000 khz AM.

COMMENG
Posts: 109
Joined: Wed Dec 18, 2013 4:30 pm
Location: Midwest

Re: Restoring a small transmitter

Post by COMMENG » Tue Apr 26, 2016 4:44 pm

The previous owner had attempted to retro-fit a replacement power transformer, which put about 750V B+ on the 6DQ5 plate instead of the circuit recommended 450V.. I got that figured out and was able to get it down closer to the 450V
No worries about high voltages with the 6DQ5. It's the 6V6 and the 12BY7 that might have flashovers with that voltage. One can increase R3 and add a resistor for the 6V6 to get higher power at higher voltage.

I would recommend replacing the electrolytics C1A, C1B, C2, and C10 since the prior transformer may have damaged them.

Also note the Pi-output network. C12 and C13 were set/selected for the frequency of operation. if going down in frequency, you may have to increase those capacitor values. And you may also have to move the coil tap as well.

Lastly, if you are feeding any type of Ham Linear do not feed it with more than 15 to 20 Watts from the Cunningham exciter.
They are Ham radio amps and the power is 400 watts
Is that input power and are the Linears Tube type or Solid-State?

Phil

Patrick De Landsheer
Posts: 7
Joined: Thu Nov 27, 2014 3:21 pm

Re: Restoring a small transmitter

Post by Patrick De Landsheer » Thu Apr 28, 2016 7:27 am

Sorry for having taken so long to answer. A friend gave me a few 1 Mhz CRYSTAL to help with the frequency changing, I know some modifications are needed but I not sure where to start. Any help? I want to switch from 1610 or 1620 to 1000 khz. Thanks.

Patrick De Landsheer
Posts: 7
Joined: Thu Nov 27, 2014 3:21 pm

Re: Restoring a small transmitter

Post by Patrick De Landsheer » Thu Apr 28, 2016 7:31 am

The linear amps have tubes

COMMENG
Posts: 109
Joined: Wed Dec 18, 2013 4:30 pm
Location: Midwest

Re: Restoring a small transmitter

Post by COMMENG » Thu Apr 28, 2016 11:13 am

Patrick De Landsheer wrote:Sorry for having taken so long to answer. A friend gave me a few 1 Mhz CRYSTAL to help with the frequency changing, I know some modifications are needed but I not sure where to start. Any help? I want to switch from 1610 or 1620 to 1000 khz. Thanks.
There is a Master Tune-Up Chart in the manual.

For 1MHz it says use Full Coil (48 Turns) and add 230 pF to the Plate Loading capacitor.

How many and what are the tube types in the Linear?

Patrick De Landsheer
Posts: 7
Joined: Thu Nov 27, 2014 3:21 pm

Re: Restoring a small transmitter

Post by Patrick De Landsheer » Wed Jun 06, 2018 6:44 pm

Hi, I'm truly sorry and I have once again to apologize for the big delay in my answers, I had lost my password among other situation like moving.

Ok yes I will try to find out about the power amp- it's an Ameritron i think the final tubes are 811.
still having difficulties to find the capacitors 230pf and 530pf here in Haiti where no one is interrested in AM anymore all the tecnicians are only doing FM now.

Thanks for any help I can find to put them on the air on 1000 khz

w9wi
Posts: 892
Joined: Tue Feb 05, 2008 11:40 am
Location: Pleasant View, Tennessee
Contact:

Re: Restoring a small transmitter

Post by w9wi » Thu Jun 07, 2018 6:24 am

Sounds like it may be an AL-811, with three 811A tubes in parallel. A copy of the manual (with schematic) is available on http://www.ameritron.com/Downloads/inde ... =ameritron.

I would be cautious about operating this amplifier at 400 watts output in broadcast duty. If it's indeed a ham amplifier it may not be designed to operate at full output continuously. (the manual says the cooling of the tubes is adequate for 100% duty cycle at 400 watts but it doesn't say anything about the power supply) Hams, the intended users, do not transmit continuously. (if a ham wants to have a two-way conversation, he has to stop talking every once in awhile & let the other guy talk:) ) That, and most ham transmissions use suppressed-carrier mode (where there is no carrier and no power during pauses in speech) or Morse Code. (where there is no power unless the code key is being pressed)
--
Doug Smith W9WI
Pleasant View, TN EM66

COMMENG
Posts: 109
Joined: Wed Dec 18, 2013 4:30 pm
Location: Midwest

Re: Restoring a small transmitter

Post by COMMENG » Thu Jun 07, 2018 2:31 pm

Patrick De Landsheer wrote:
Wed Jun 06, 2018 6:44 pm
Hi, I'm truly sorry and I have once again to apologize for the big delay in my answers, I had lost my password among other situation like moving.

Ok yes I will try to find out about the power amp- it's an Ameritron i think the final tubes are 811.
still having difficulties to find the capacitors 230pf and 530pf here in Haiti where no one is interrested in AM anymore all the tecnicians are only doing FM now.

Thanks for any help I can find to put them on the air on 1000 khz
Parallel common value capacitors: Foe example, use a 220 pF and a 10 pF (both at 2 kV) = 230 pF. Let's say you have a need for a 530 pF capacitor but you have only a 330 pF capacitor. 530 pF - 330 pF = 200 pF. In other words a 330 pF paralled with a 200 pF capaciotr = 530 pF.

Mouser is a good place from which to order caps: https://www.mouser.com/All-Manufacturer ... rs&FS=True

Any more news on the tube complement and number of tubes in the Linear Amplifier. :?:

COMMENG

Patrick De Landsheer
Posts: 7
Joined: Thu Nov 27, 2014 3:21 pm

Re: Restoring a small transmitter

Post by Patrick De Landsheer » Fri Jun 08, 2018 4:13 pm

Thanks for the comments and the advices I will try the mouser site to see if I can obtain those capacitors.

For the linear info. I would have to open the amp to see what is inside. I'm sure He had done some modifications. I'll try when I have the opportunity to go on the site where they are.

But, I was hoping to be able to listen at least the carrier signal on the 1000 khz frequency by putting a 1mhz crystal in the oscillator... but nothing at all!

COMMENG
Posts: 109
Joined: Wed Dec 18, 2013 4:30 pm
Location: Midwest

Re: Restoring a small transmitter

Post by COMMENG » Wed Jun 13, 2018 1:58 pm

Patrick De Landsheer wrote:
Fri Jun 08, 2018 4:13 pm
Thanks for the comments and the advices I will try the mouser site to see if I can obtain those capacitors.

For the linear info. I would have to open the amp to see what is inside. I'm sure He had done some modifications. I'll try when I have the opportunity to go on the site where they are.

But, I was hoping to be able to listen at least the carrier signal on the 1000 khz frequency by putting a 1mhz crystal in the oscillator... but nothing at all!
Normal testing procedure is to check these items

1) Make sure you have good tubes.

2) B+ on each Plate and screen without the crystal. Plate voltage is about 445 volts, screen voltage is about 200V or lower depending on stage.

3) Then with the crystal in and a scope check for RF on each control grid and plate. Make sure you are using a X100 probe and a 1000 pF capacitor in series with the probe tip.


COMMENG

Post Reply