Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Bandmaster VFO output level




 
The AM Forum
October 02, 2023, 03:08:21 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Bandmaster VFO output level  (Read 5795 times)
0 Members and 1 Guest are viewing this topic.
stevef
Guest
« on: October 30, 2010, 06:29:54 AM »

What is the output voltage of a Harvey Wells Bandmaster VFO?   Or in other words, how much VFO output do I need to feed a TBS-50 transmitter?

Thanks,

Steve
KK7UV
Logged
WQ9E
Member

Offline Offline

Posts: 3271



« Reply #1 on: October 30, 2010, 07:45:58 AM »

Steve,

I have never measured the output of my Bandmaster VFO but before I got it I used a Knight Kit VFO to drive the TBS-50 with no problem and had more than enough drive.  I think any of the classic tube type VFO units will work fine.
Logged

Rodger WQ9E
stevef
Guest
« Reply #2 on: October 30, 2010, 08:08:15 AM »

Thanks.   I was thinking of trying to use my BC-221 followed by a 6AG7 amplifier stage that I can use as a VFO.  Just thinking about what kind of output level I could expect and if it would be adequate.
Logged
WQ9E
Member

Offline Offline

Posts: 3271



« Reply #3 on: October 30, 2010, 08:28:27 AM »

With the 6AG7 amp it should be more than adequate.  I would suggest designing in a gain control for the 6AG7 stage so you don't end up with too much drive to the 6AQ5.  With the Knight VFO and its 6AK5 buffer/amp stage I never advanced the drive control very far on the TBS-50. 

On 80, your BC-221 might have enough drive without an amp; have you tried it yet to see what happens?



Logged

Rodger WQ9E
KC4VWU
Member

Offline Offline

Posts: 669


« Reply #4 on: October 30, 2010, 11:16:58 AM »

BC-221?! Wow, the VFO will be bigger than the transmitter! Just kidding... it's a great idea.

I use a VF-1 with my TBS-50D and it provides plenty of drive; although I never really checked it's outpoot voltage before I hooked it up. After I get past a few more projects, I'm going to try modding a Siltronix Model 90 VFO to use with it. I'm also going to look into moving the blocking cap as to isolate the tank from DC potential. It seems to be plagued with arcing issues no matter how much I try to clean and keep the topside free of dust. A couple weeks after the cleaning routine, the arcing just starts all over again.

How does your Bandmaster look? I have two which were in pretty poor shape and one is operating right now with a homebrew front panel until I can figure out a good process to re-silkscreen the original. I also have a H-W VFO to match with which one of the pair that turns out the best to restore.

73, Phil
Logged
stevef
Guest
« Reply #5 on: October 30, 2010, 01:38:04 PM »

Well I got the 221 for a steal ($10) and it is in terrific condition and is amazingly stable after a 15-min warmup.  I thought I'd try to put it to work as a VFO and see what happens.

I attempted to use the 221 last night for a VFO on 80m but could not get any grid current reading on TBS-50.  My initial thought was that the 221 output might be too low.

My TBS-50C is in very nice condition.  I also re-arranged the tank for parallel feed also.
Logged
WA2IXP
Member

Offline Offline

Posts: 48


« Reply #6 on: October 31, 2010, 08:29:48 PM »

Steve,
   I have 2 lm-1 frequency meters which are very similar to the bc-221 that I use as vfo's. They are quite stable but do require a stage or two of amplification. One uses a untuned pentode driving a 6ag7 with tapped plate coil for output on 160 and 80 mtrs. Its link coupled to the cathode of a crystal osc. A 6f6 I think. Plenty of drive. I used the link because I wanted to send the power and rf through several feet of shielded cable so the vfo could be on the desk.
   The second unit has several stages of multipication in it switched with small relays and has a few watts output on 3.5, 7 and 10.5 mc (for 15 mtrs). Works but really has too much stuff jambed into small area. Ran the heater for the osc. tube on dc because of hum on 10 and 15 mtrs.
   If I was doing it again I'd buy one of those digital vfo kits (check e-bay) and add a stage to bring the output up enough to drive the grid through a stepup transformer. There cheap and very stable.
   I had a tbs-50 deluxe w/ vfo which I think went to carl  WB2EYE years ago. Was only a single tube with maybe a regulator. Was very shakey at best.
    Just re-reading the later posts and a gain control was mentioned-Yes you'll need that. I varied the screen voltage on the 6ag7.
 Jay-                                                   
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.136 seconds with 19 queries.