Hammarlund receiver clean up advice needed - Page 1
Forum section: electronics / beginners

author: BillWojo
author_rank: Regular Contributor
timestamp: July 22, 2014, 09:52:20 pm
content: I was at a customers shop today and under the foremans desk was an old tube radio. Turns out it's a Hammarlund HQ110A ham radio receiver. Missing the outer cover but all 11 tubes are still intact. Gave him 10 bucks for it, figured it's cool looking and maybe it will work with a little cleaning up.This thing is filthy, who ever had it must have spent years sitting in front of it smoking. Front panel is yellow with tar. The chassis is nasty also. Underneath not to bad.What I was thinking is to give it a good spray down with simple green and use a soft bristle brush to scrub it well followed by a good rinse with the garden hose. Blow dry and than bake it in the oven for 6 hours or so at 120F to dry out all the areas that the air gun misses.From what I can see, there is only one electrolytic cap, the rest are ceramic disc type. I'll power this up slowly on a variac after it's throughly dried out.Does my game plan sound reasonable or am I looking for trouble?ThanksBillWojo

author: BillWojo
author_rank: Regular Contributor
timestamp: July 23, 2014, 02:07:18 am
content: Well, I decided to go easy on it tonight. I spent a little time rewiring the variac that I picked up at a flea market. It's old and in a wooden box with the insulation crumbling off the wires for the cord. So I made up a new cord and tested it, works fine. Grabbed the receiver and just blew it out with compressed air. Figure a good cleaning can come later. Hooked up the receiver to the variac and slowly increased the voltage over about an hour. Looks like most if not all the tubes light up. Have no speaker or antenna to try it out yet. Started to clean the face plate with just a damp rag, sure is a handsome looking unit. I'll spend some time picking away at getting it clean and start looking for a speaker. I read online that it uses a 3.2 ohm speaker. What would happen if I used a 8 ohm speaker? Haven't played with one of these since I was a little kid.BillWojo

author: BillWojo
author_rank: Regular Contributor
timestamp: July 23, 2014, 05:06:41 am
content: Did some research and found that the output for the audio is 1 watt. Looking for a speaker but I think most modern speakers are 8 ohm and this calls for a 3.2 ohm speaker. Is there anyway I can use a 8 ohm speaker with this?ThanksBillWojo

author: Unknown
author_rank: Unknown
timestamp: July 23, 2014, 05:49:16 am
content: Speaker impedances are nominal, not some hard-and-fast value. Don't sweat it. Assuming it's got a fairly standard for the period output stage, then 8ohms should be fine. Grab a car radio speaker if you're worried; they're usually 4ohms.Congrats on a nice old set. Ham bands only I believe, 6m & down, but still nice.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 23, 2014, 05:55:15 am
content: I doubt that the Hammarlund will care whether it is feeding a 3.2 Ohm or 8 Ohm speaker.The audio output stages of these things weren't highly stressed.I've only ever had a look at one Hammarlund,which was a pre-WW2 "Super-Pro",but I think they are all similar.Some of the Electrolytics may not be easily recognised as such,as they may be chassis mount units.I'm not certain if Hammarlund always used a power transformer.i'm pretty certain that the "Super-Pro" had one,but if this is a cheaper model,it may not-----so be careful!Google is your friend---------you should find quite a lot on these radios.P.S Just found this on Youtube:_It shows that your radio is a lot younger than the Super pro,& answers my question about the transformer.Re the Electrolytic---I think it is probably a multiple can with several caps inside!

author: BillWojo
author_rank: Regular Contributor
timestamp: July 25, 2014, 08:30:39 pm
content: I'm going to a local ham meet in the morning, my first one. I'll look for a vintage speaker while I'm there. I did some research and the big electolitic capacitor is indeed a 3 part cap. Specs say it's a 20mf 450V X 2 and a 25mf 50V can. I suspect a direct replacement isn't possible to find or is it?ThanksBillWojo

author: Unknown
author_rank: Unknown
timestamp: July 26, 2014, 12:34:04 am
content: Quote from: BillWojo on July 25, 2014, 08:30:39 pmCheck out the antique radio & tube amp shops on the net e.g.RadioDaze,Tubes and More, etc. You might be lucky - and the exact capacitance values likely aren't critical anyway. 20/20/20 & 30/30/30 were common values, and either of those would be fair substitutes. Realistically, you pick whatever's got the right physical size & mounting, then choose one with the nearest values & voltage ratings.The other option is to replace it with modern electros. It's pretty common to disconnect the old one, leave it in place for appearance's sake, and install new caps under the chassis. Alternatively, if they'll fit you can carefully pry open the can, clean out the old caps & pitch/wax/whatever they filled the can with, & install the new caps inside.

author: Robby
author_rank: Newbie
timestamp: July 26, 2014, 03:21:54 am
content: Nice old rig, turned down an offer to buy one a few years back. Just didn't have the time to work on it I guess.Some guys will not bother to get an original cap. Neither would I. But one can gut it and use it to hold newer caps (not a bad idea) and make it look and work as though it was an original replacement. Besides, if you were to get an old replacement, who is to say that it isn't any better than the one you took out?IIRC, there is a guitar amp builder in S.California (think his last name is Blankenship) that restores old tweed Fender amps and has a supplier for new/old stock multi-caps like yours. Can probably find him through YouTube and send him a note . . .