Started in on a 41-300 - Printable Version
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+--- Thread: Started in on a 41-300 (/showthread.php?tid=17076)
Started in on a 41-300 - Radioroslyn - 07-29-2017
Tested tubes and half were pretty weak. Recapped soldered new ecaps under chassis
rather than restuffing as they are difficult to remove. Push button assy has to come out remove them. Original off/on switch is bad so am sourcing a replacement. Output transformer is open but have a suitable replacement on hand. Wiring is pretty good but need to rewire the lamps and replace insulators. Maybe this afternoon I can give it a try.
RE: Started in on a 41-300 - sam - 07-29-2017
well its about time
oooh my back
sam
RE: Started in on a 41-300 - Radioroslyn - 07-29-2017
Dug up a hammond 125 series output transformer but is too large to mount under the chassis. Next is a Thordarson 24S11 fits very nicely but have to do some guess work to come up w/the proper match and feedback point. Have plenty of options as it's a mulitimatch. Also found what I think will be a good replacement for the off/on switch. Should be getting it in the next few days.
RE: Started in on a 41-300 - Radioroslyn - 07-29-2017
I know that yous guys like pics so here's a pic of the underside. The opt is just tacked in cause unless I'm a very good guesser or just dumb luck I'll be playing w/the connections to get the matching and phasing correct.
I did change the wiring a bit to be able to solder in the input cap and not have it bouncing around. It's the one up at the top center. Left most of the rubber wire entacted, under the chassis it seems to be pretty good on the top not so much. I was a little surprised that the is some cloth covered wire in the set too.
Was cleaning up the dial glass and notice that it's graphs are applied to both sides giving a two dimensional look. Pretty kewl!
Have yet to pull out the spkr from the cabinet then I can play w/ the op circuit. Hopefully I'll have it working tonight and be able have a listen to the local otr programs that are local on the air.
Hate the line cord going for black or brown!!!
RE: Started in on a 41-300 - klondike98 - 07-29-2017
Enjoying to show!
RE: Started in on a 41-300 - Radioroslyn - 07-29-2017
Tnx!
So I got it playing and noticed that the volume and tone control were noisy this started an adventure as they are difficult to get at. Have to remove the p/b assy and the thumbwheels which are kinda tricky. Finally got the pots apart hit them w/some wd-40 and now they behaving nicely.
After I reassembled the vol/tone controls I powered it up to check to hear if I had made improvement. Applied ac current and after about 20 sec smoke bellowed out of the 1st IF transformer along with the 80 glowing RED. Well that's new! I thought I had gotten rid of the curse of the 660L. Checked the resistance along the HV path and didn't find anything that was shorted. Did find a blob of loose solder perched on of the wires on the IF transformers but wasn't shorting any thing. What it was was a bit of rubber wire that was arcing to the chassis. Wasn't a short till you put HV on it. wire looked good on the top, it wasn't very apparent. I guess I need to replace some more rubber wire.
Going to set it aside till the switch comes in, now I have it working w/the p/b assy out. Will have to fabricate a bracket for the switch. Plays well and is good sounding even w/o the feedback connected.
Otr will be heard on the 116X tonight.
RE: Started in on a 41-300 - Radioroslyn - 08-03-2017
Off/on switch came in the other day. Mounted it to a small piece on brass and soldered it to the PB assy. Works dandy.
When I was working on it before I didn't notice that the volume and tone controls didn't do what they are supposed to do. Volume control would raise and lower the volume some but it also changed the tone some what. The tone control did very little. Started looking the vol and tone circuit to see if I miss wired something when I was cleaning the pots. That circuit will make you dizzy trying to follow it around. Everything looks OK. After some head scratching I figured it out. The volume control gets it's ground connection thru the secondary of the output transformer (feedback loop) I had left it disconnected till I was ready to get the proper phrasing set up. Checked phase it was backwards fixed that and with loop connected the volume control and tone are back working.
Not real happy with the set up as is. The loop really drops the output down. I'm waiting on some tubes to come in, the 37's were pretty weak so maybe replacing them will help. Did use an external audio source to supply a signal to it and had to drive it w/ a fair amount of audio to get a fairly loud output from the spkr. May revisit the tap arrangement the opt.
Was listening to it on the BCB and noticed at the low end the sensitivity was poor and was getting some images. Could be a tracking issue. Thought it was a good time set the oscillator. Couldn't hear the local 560kc station. Turned it off and went to grab a small screw driver / check the service info for which screws to dittle with. Turned it back on and no reception. Audio is working and I used my little counter to check the lo it's ok so either the mixer or IF has taken a powder.
Going to take a break till the tubes get here, a few days and start troubleshoot again.
RE: Started in on a 41-300 - Radioroslyn - 08-03-2017
Ok so it was bugging me, went and checked the IF and it was ok but the mixer tube plate voltage was low it was abt 30v. Bad 10K resistor ?? No it was abt 15k. Bad #35 ( goes from the HV to the cathode of the mixer). Didn't replace it at first as it was a fairly new party .01@1600v. Shorted. Cut it out voltage went right up to 200v where it should be. Fixed that all up and now it back working but volume is not quite what I think it should be and has very poor sensitivity at the low end of the bcb. Thinking weak XXL tubes.
RE: Started in on a 41-300 - Radioroslyn - 08-09-2017
Tubes came in this morning. Replaced the XXL's and 7B7's and it improved the sensitivity greatly, now I can hear stations at the low end of the bcb. Retouched the alignment. Replaced the the three #37 tubes and helped a little. All of these tubes were showing abt half way up on the replace scale of the I-177 tester. Volume is better w/the replacement RF and IF tubes play fairly loud now.
Ended up just grounding the feedback loop, sound great and has good volume. When I had it hooked up before it would either oscillate or cut the audio level down badly. Fixed a few small tears in the cone. Seems pretty brittle added some rubber cement along the edge of the cone.
It just needs the eight little wood screws that hold the escutcheon on, they were miss where I got it and an amber or red lens for the front pilot light.