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Author Topic: 32V-2 driving a linear, how to key the amp???  (Read 13292 times)
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KJ4OLL
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« on: June 14, 2015, 07:18:07 PM »

Hi,
I have a 32V-2 and want to drive an external amplifier with it.

I read the 32V-2 manual, but the part where it says to use terminals 4,5 for "500 ohm audio output"
is not what is needed to drive the linear I have.

The manual also says terminals 2,3
" Connect to supply unmodulated high voltage to V105"
(V105 is the 4D32 final amplifier)


But the linear just needs a simple contact closure make/break to key up:
The linear keying info is:
Amplifier Keying Parameters (ALPHA 374A RELAY jack)
UNKEYED KEYED
25 vdc    75 ma

Kind of baffled as to how to approach this, probably need another relay cascaded
off of the TX/RX relay? Or HuhHuh



Thanks
Frank
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W1ITT
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« Reply #1 on: June 14, 2015, 08:04:53 PM »

While you can go with a fancy logic driven sequencer, the cascaded relays will work well.  The main thing is to have the amplifier transferred and switched on before the drive power starts impinging on it.  And the drive needs to stop before the amp is shut off.  The make and break times of relays are good to know, and usually found in manufacturer's data if you buy new ones. Depending on what relays you choose, they can be almost silent, or provide a satisfying clunk.  Any extra contacts can control a receiver, or even one of those tacky On The Air signs from the sixties.
Be careful with that Alpha 374.  It doesn't take much to drive it.
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KJ4OLL
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« Reply #2 on: June 14, 2015, 08:36:40 PM »

Found out in testing about the drive!
Connected the Flex to the Alpha & dummy load to test.
Flex makes about 25 watts in AM, WAY too much drive for the Alpha.
About 10 watts input should be close.
I have the 32V-2 in the "low voltage" setting, max about 70 watts carrier.
Have a BIRD 100 watt 10db attenuator, will start with that.
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WD5JKO
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WD5JKO


« Reply #3 on: June 14, 2015, 08:53:26 PM »

Found out in testing about the drive!
Connected the Flex to the Alpha & dummy load to test.
Flex makes about 25 watts in AM, WAY too much drive for the Alpha.
About 10 watts input should be close.
I have the 32V-2 in the "low voltage" setting, max about 70 watts carrier.
Have a BIRD 100 watt 10db attenuator, will start with that.

   Good! You will need that attenuator. If that Alpha is a two holer (pair of 8874's), then you got 800 watts of plate dissipation. If An AM linear is 33% efficient, that means it takes 1200 watts DC input to make 400 watts carrier output with sufficient headroom for 100% modulation. If you want extended positive peaks, then figure on 25% efficiency. So after derating a bit for adding headroom, and to allow the positive peaks to extend up a bit, you have a 200 watt carrier level AM station.

  That is a lot of trouble for a 3db boost in signal, but hey...it should work. Maybe your Alpha is a 3 holer (3 8874's). If so, then with 1200 watts of plate dissipation (like a hair dryer on high power), your good for at least 300 watts AM with room for more.

Jim
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MikeKE0ZUinkcmo
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« Reply #4 on: June 15, 2015, 07:05:10 AM »

My method is frowned upon by many, but I just use carrier operated relays in amplifiers. I've installed them in Gonset, Dentron, and National amps, and feed them directly into an old Viking T/R relay via a patch panel.  Takes about a watt to trip them, and Removes the constant interface hassles between extinct equipment makers.

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Mike KE0ZU

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W3GMS
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« Reply #5 on: June 15, 2015, 11:08:46 AM »

My method is frowned upon by many, but I just use carrier operated relays in amplifiers. I've installed them in Gonset, Dentron, and National amps, and feed them directly into an old Viking T/R relay via a patch panel.  Takes about a watt to trip them, and Removes the constant interface hassles between extinct equipment makers.



I like you scheme Mike!  Makes it very simple especially when you have a bunch of rigs. 

Joe-GMS
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K1JJ
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« Reply #6 on: June 15, 2015, 12:02:43 PM »

My method is frowned upon by many, but I just use carrier operated relays in amplifiers.


Hi Mike,

I'm curious why it is frowned upon? Is it because there is no PTT operation available - IE, on ssb (and especially on cw) it would be clicking the amplifier on and off at a rapid rate?  I know they use this type circuit quite often in CB linears.  

Come to think of it, a PTT mode could  be added by keying the Q1 FET / relays with a separate hand switch pole that keys the exciter.

Other than that, on AM, what would be the disadvantage, if any?   The only other thing I can think of is the sequencing. We usually want the amplifier (load) to come on first before drive is applied. In this case, drive comes on first....

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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MikeKE0ZUinkcmo
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« Reply #7 on: June 15, 2015, 03:37:04 PM »

Don't know why, but some folks just don't like the idea of carrier switching.   It's to "VHF" or to "CB" or something I guess.  

My statement regarding a "Viking relay" is incorrect in that I actually use a the ole Johnson 250-39 T/R switch and pick the amp output off ahead of any internal antenna switching, because its not needed, as the load (or antenna) is always present, presuming of course, no operator error.   AS for CW, a little "hang" could be introduced to facilitate most any speed.

This is  basically how I handle interface on the radio bench.   This allows me to mix n match at will.   Receivers are modified to mute, as it was originally intended to be done, with small interface breadboards in each one.   +5 at the radio mute buss is "TX" and ground is "RX".   I like to keep the impact of mods as close to "zero" as I can, that way they are easy to return to stock.   I also generate documentation for each piece of gear, kept in a dedicated note book.

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« Reply #8 on: June 15, 2015, 05:01:05 PM »

I'm another fan of the cascade relay scheme. It has worked flawlessly here and it's cheap and simple to do. At this point in time relay C of my relay arrangement is toggled between several different rigs on the bench.

Rob W1AEX


* cascade relays.jpg (52.91 KB, 1226x869 - viewed 510 times.)
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w4bfs
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« Reply #9 on: June 16, 2015, 09:56:04 AM »

back to the original question ... connections 22 and 23 carry 120vac on ptt activation for external ant relay ... terminals 8 and 9 for low voltage dc relay ... check your manual for potential build differences ... verify with multi-meter ... please be careful
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KJ4OLL
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« Reply #10 on: June 21, 2015, 11:49:27 AM »

Hi,
Using boatanchors is good "character building" training for me.
I must remain patient.
I must not throw things and have a tantrum.
Kicking Leo the wonder dog is definitely out.

Found the perfect attenuator (6db) yields 17 watts input to the ALPHA.
Nice 220 watt carrier from the ALPHA.

Now the 32V-2 won't modulate.
Makes fine carrier.
Put the 6SL7 Audio Amplifier tube in the TV-10, one side reads adequate micromhos, the other side is dead.
Same for the 6SN7 Audio Driver.
One of the 807 Modulators had a weak reading.
I changed them all, still no modulation.
So today's mission is to check more toooobs.
This 32V-2 has been absolutely reliable for the past few years, but as part of the linear project, I had to move the 32V-2 around a bit, old tubes might not like vibrations.
Frank
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K1JJ
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« Reply #11 on: June 21, 2015, 12:53:32 PM »

Hi Frank,

If you get done with the tube testing and it still doesn't work, key it up into a dummy load and then put a small 1 KHz audio tone  into the audio input. You might need an attenuator to keep from overdriving the mic input. Be careful, since the mod transformer is involved.   Use a scope probe (X10) and scope rated for enough voltage to look at each audio stage, grid to plate, grid to plate until you arrive at the modulation transformer output.   Find the stage where the signal stops or gets all distorted - divide and conquer.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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There's nothing like an old dog.
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« Reply #12 on: June 21, 2015, 05:27:49 PM »

I guess my question is, if the unit was working OK and then not.  After replacing the bad tubes and still no joy - (dreaded question) have you check the modulation transformer to see if it is OK?

Al
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WD5JKO
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WD5JKO


« Reply #13 on: June 21, 2015, 06:47:50 PM »


   You might stick to the exciter all by itself until it is working proper....then once the exciter is good, click on that big Alpha.

Jim
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KJ4OLL
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« Reply #14 on: June 21, 2015, 07:13:12 PM »

Was hoping to get to test more tubes today, but changing the alternator in the 1985 300TD took all day - over 100 degrees on the concrete pad, this old guy had to take it slow and hydrate/cool off frequently.
I fear the Modulation transformer in the 32V-2!
Even though the HV is always set to the "600" position (low voltage option), and the modulation transformer has a box fan on it, I know they can be a problem.
If it is the Modulation transformer, would it be best to send it to Gary for a rewind, or order a new one from Hammond?
Cost is the same either way.
Thanks,
Frank
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WD5JKO
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« Reply #15 on: June 22, 2015, 10:16:15 AM »

   Frank,

   before condemning the modulation transformer, I wonder if you can decouple the 32V from the amplifier, hook to a good dummy load, and do some checks? Heck, the lack of positive peaks could be insufficient grid drive to the 4D32, or a bad 4D32..

Good online 32v reference material:
http://www.qsl.net/wa5bxo/32v3/

    I am not sure how easy it would be to make some voltage checks, but perhaps you can measure the modulator bias and screen voltage when keyed up on AM? Is the idle current proper? If good, and you have a scope, and an audio generator, maybe you can inject a sine wave of sufficient amplitude to get 50% modulation. Look at the modulator grid waveforms, and the RF output modulated envelope. You will need a 10X low capacitance probe for these measurements. If you have a 100X probe, then you could look at the modulator plates.

   As with any high voltage measurements such as this, be careful, and don't be alone.

   If something is breaking down on modulation peaks, consider that the modulation transformer is only one possibility.

Jim
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KJ4OLL
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« Reply #16 on: June 22, 2015, 06:52:50 PM »

Hi,
Thanks for the tips and advice!
I am looking forward to learning the 32V-2, troubleshooting can be a good teacher for me.

Came home from work, took the required nap (65 year old needs recharge), woke up and started collecting test gear.

1khz sine wave @10mv, check.


Made a cable to inject the signal into the 32v-2 mic jack.


32V-2 powered off, just checked that the signal made it OK through the first cap & resistor, to the first tube socket.



Next is to power up the 32V-2 into a dummy load, dust off the HP 410C and start looking for voltages!

Thanks,
Frank
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Jim, W5JO
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« Reply #17 on: June 22, 2015, 08:24:44 PM »

Did the output impedance of your source equal the input impedance of the load?
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Steve - K4HX
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« Reply #18 on: June 22, 2015, 10:08:51 PM »

With that set up, you should be able to trace the audio all the way through the system or find where it stops. Good luck.
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KJ4OLL
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« Reply #19 on: June 23, 2015, 08:12:15 PM »

Hi,
Modulation is fixed!
While doing tube testing, I discovered V302, one of the 5R4GY HV rectifiers, was not connected to the socket.
Somehow, all the "fingers" that hold the pins had relaxed, and nothing but gravity was holding the tube in place.
No mechanical or electrical contact between the pins and socket at all.

Squeezed the socket fingers back together, now the tube works fine, and so does the modulation.
No idea how/why the HV rectifier can effect modulation in this way.

Now I am trying to figure out if the linear is being driven properly, by looking at a software (REA) display of the ALPHA output.
Frank
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