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 Post subject: HQ-170A Filter Cap Question
PostPosted: Sep Sat 22, 2018 1:21 pm 
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Location: Yardley, PA 19067
I picked up this week what seems to be an earlier production of an HQ-170A (doesn't have the VHF tag on the faceplate). Although there was evidence of it sitting around in someone's basement for quite some time (crud on the chassis, mouse residence, etc.) I was able to clean it up nicely, swap out the 7 paper caps, and most of the resistors measured ok. Plays very well in all modes and although it could benefit from an alignment it appears to be pretty darn close.

The one concern I have is the filter cap. As standard practice when I work on a radio I replace the filter caps with either a new can or caps mounted underneath the chassis if sufficient room. In this case it clean one of the previous owners made some changes to the power supply. First, as shown in the pics C82A and C82B are shorted together. Second, at the junction of diodes CR1 and CR2 there is additional wiring along with a pair of 8uf @450V electrolytics in parallel. The additional wiring goes to L6 which I believe is an 8H filter choke ( I think this is a standard component in the 170, 170A and 180). I'm trying to understand why this was done. Carl (WA1KPD) and I speculated that possibly L6 bit the dust and the extra capacitance was needed (although 16uf seems to be negligible) while the 100uF (combined C82A and C82B) would help. Why not just add a 300 to 500 ohm resistor? Or did the previous owner try to solve two other issues...(a) add the electrolytics in parallel to deal with the low level AC hum typical of Hammarlund receivers and (b) quick recourse to a weak filter cap without replacement.

The receiver works very well with no discernible hum, audio distortion, etc.


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Thoughts?

Thanks...Harry WE1X


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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Sat 22, 2018 1:45 pm 
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Harry,

My best guess is the previous owner tried to reduce the B+ by reducing the value of the input filter and then added more capacitance on the output side (via paralleling the two standard capacitor sections and using this on the output side of the choke) to make up for the reduced input filter capacitance. The lower level of input filter capacitance (the two 8uf in parallel) result in lower peak charging current and lower B+ but also less filtering. Chokes very seldom short across the winding which is what would have to happen to reduce the inductance; typical failure mode is either they go open or short to core and in either case that choke would have to be taken out of circuit. My guess is that the choke is just fine. I would restore it back to the way it was when it left the Hammarlund factory instead of following the lead of hammy hambone who thought he knew more than the Hammarlund engineer who designed the receiver.

The presence or absence of the VHF tag doesn't reflect when it was produced; the VHF version was a slightly modified version from the factory with a converter for 2 meters that also operated as a preamp for the existing 6 meter coverage. This nuvistor design provided a pretty usable VHF setup, especially for its era.

Rodger WQ9E


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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Sun 23, 2018 1:55 pm 
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Rodger,

As always, thanks.

Sometime next week I'll open it up and make the changes.

One other question. This 170A has the clocks that doesn't work. Before I do a search on probable cause and repair do you have any experience doing this? I'm debating whether it's worth the effort. I do know if I move the knob below the clock it will shut off or turn on the radio. But the clock itself is not working.

thanks again,

Harry


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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Sun 23, 2018 2:29 pm 
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Harry,

You are welcome!

Sometimes the clock motor will respond to lubrication. I used the method I first read in an old Radio and Television News as explained by prolific writer John Frye. You need to have some light synthetic oil available and put on a glove to protect your hand. Hold the clock motor up against an incandescent light bulb or other moderate heat source until it is very warm and then pull it away and feed oil through the lubrication port if it has one or otherwise form a pull around where the shafts for the clock hands exit the body. As the motor case cools it will suck in the oil. You will need to repeat this several times.

The above will usually quiet a noisy clock motor but if it is totally frozen it may not work and if the winding has gone open then a transplant is about your only option.

There have been a number of people over the years who sold quartz replacement movements for these. Most (maybe all) don't support the timer function but the upside of the quartz movement is you wouldn't have to leave the receiver plugged in at all times.

Rodger WQ9E


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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Sun 23, 2018 3:34 pm 
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Harry,

I have a Hammarlund that had a bad clock motor. The Telechron clock uses a very common motor that was in a huge number of their clocks. I just found a cheap used Telechron clock on EBay and took its motor and substituted. Very simple and easy fix. I have a little more detail in one of my threads from a year or so ago.

viewtopic.php?f=5&t=328794&hilit=Telechron

Norm

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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Mon 24, 2018 1:26 pm 
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Location: Yardley, PA 19067
Hi Norm,

Thanks for the tip. Will check it out.

Given I probably won't keep the 170A connected to a live AC line all the time a working clock is probably self-defeating. With that said, it would be nice to have a complete working unit.

BTW my warm up time for little drift is about 60 to 90 minutes. Don't know if that's "typical" but it seems awfully long. I swapped out the 6BE6 in the first mixer and that helped. Tried a couple of 6C4s as well will little improvement. Don't recall my earlier 170 requiring that amount of time to be stable.

Harry


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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Mon 24, 2018 3:30 pm 
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Harry,

60-90 minutes for warm-up does seem to be a long time. With the main and band spread capacitors fully meshed check that the rotor plates are centered between the stator plates because offset here will decrease thermal stability. This is adjustable via the thrust bearing and the oscillator section is the most critical so use it for centering.

Does it drift badly on all bands (drift generally is more noticeable as frequency increases but it shouldn't be a huge jump band to band).

I don't like leaving vintage gear having power available when unattended either. If you do so make sure that the power cord is in excellent condition and the proper fuse is installed in the line/load side of the cord and prior to everything including the line bypass cap and power switch. I have replaced three power switches in vintage gear where there was a carbon track from live to ground.

Rodger WQ9E


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 Post subject: Re: HQ-170A Filter Cap Question
PostPosted: Sep Mon 24, 2018 4:01 pm 
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Joined: Jan Wed 20, 2016 7:43 pm
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Location: Yardley, PA 19067
Rodger,

The power side of things look good other than the hammy hambone thing done earlier. Regarding that, I beginning to wonder if he did anything else. Bit fearful of starting to restore it with a new filter cap can out of fear I may have missed something and whoa...there goes the transformer.

I noticed on sideband there would be about 5 kc drift over the 90 minute period.

Will take a look.

Thanks for the tip.

Harry


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