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Author Topic: Low RF Out on Collins 32-S1  (Read 2026 times)
KG4ABA
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Posts: 15




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« on: November 06, 2017, 08:04:58 AM »

Everyone's been so helpful on here...thought I'd give it another whirl...got my Collins rigs and enjoying them, except I'm not getting more than about 40 watts out according to my wattmeter on 80 meters...haven't checked any other bands.  Wattmeter is modified to show avg. and peak, and seems to show correct outputs on all other rigs and my amp in the shack, so I'm assuming that's not the issue.  Just replaced the finals (6146) in the 32-S1...Was tuning up on "lock key" setting and blew a fuse in the power supply, replaced that...so, guess I'm drawing a lot of power for the transmitter, but don't seem to have much RF out according to wattmeter and Heathkit SB 610 monitor...suggestions?
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K1ZJH
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« Reply #1 on: November 06, 2017, 10:09:10 AM »

No need to guess regarding power. That is why the device is metered.

What is your plate current when tuned up for full output?
Is there grid current showing during tune up?
Is the bias set per the manual?
Are the power supply voltages okay?
Did you neutralize the PA after replacing the final tubes?

Pete
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VK6HP
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Posts: 184




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« Reply #2 on: November 06, 2017, 10:29:10 PM »

It's critical you check the other bands, as well as thinking about the issues mentioned by Pete.  Identifying it as just an 80m problem, or an all-band problem, leads you to different entry points in the trouble-shooting.

If it's just an 80m issue, look first at the bandswitch and associated assembly.  My 32S-3 hadn't had a lot of use below 20m in its previous life and careful contact cleaning cured an annoying drive intermittency, identified by low grid drive on 80m when tuning the exciter.    

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KG4ABA
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« Reply #3 on: November 07, 2017, 07:32:38 AM »

Haven't checked other bands, will do so when I'm home for lunch...

Grid current at lock key is mid scale, plate current is 300 ma

I haven't adjusted bias at power supply, nor have I neutralized tubes, just put them in...

Been a long time since I had tube equipment so a big learning curve for me, as you can tell...
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KG4ABA
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« Reply #4 on: November 07, 2017, 01:08:51 PM »

Found out I wasn't dipping plate current properly...
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K1ZJH
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« Reply #5 on: November 07, 2017, 05:58:10 PM »

Good news!  Thanks for letting us know what the problem was.
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KG4ABA
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Posts: 15




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« Reply #6 on: November 08, 2017, 12:45:07 PM »

OK...couple of things contributed to my problem (1) my inexperience and (2) my procedure, and possibly low Rcvr osc. output...noticed on You Tube videos guys tuning up the 32-S1 always with "trans vfo" rather than "rcvr vfo" selection...got on the phone with a guy who was my chief engineer at broadcast stations where I worked...we went through correct tune up procedures, grid and plate current settings, dipping the plate current, etc.  Long story short, I'm getting plenty of drive from the "trans vfo" and not nearly enough from "rcvr vfo"...so, will always tune up with transmitter pack and vfo, sync both rigs, and probably get some tubes for the rcvr vfo and 1st mixer to see if I can get proper drive out of it...anyway, I'm now a happy camper, got output I need on wattmeter to have real qso-s...thanks for your help!
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VK6HP
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« Reply #7 on: November 08, 2017, 05:02:08 PM »

There's a lot on the Collins Collectors Association web site about the cabling between the TX/RX units.  Without reproducing it here, there are considerations of cable type and length to ensure that the best loading and levels are obtained.  Just as a very first check, make sure you have some decent RF cable and that it's about 4' long.  My units work well with some legacy RG58 jumpers that came with the TX but you can read about the better options.   What you really want to avoid are audio type cables, which are bad news in the critical oscillator connection application.
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KG4ABA
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« Reply #8 on: November 09, 2017, 09:56:53 AM »

Thanks...I've been looking at cable sets on eBay to see what's out there...
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