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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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11th Jun 2010, 8:19 pm | #21 |
Dekatron
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Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
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Re: Lafayette HE-40 receiver
Ah yes thanks Chris that sounds very much "on track" with what my friend Patrick deduced. Dave W
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12th Jun 2010, 10:40 am | #22 |
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Re: Lafayette HE-40 receiver
Hi chaps and ladies, the good news is that -rather than spend a gallon of petrol to Maplin and back I ordered a couple of 330ohm metal film resistors, arrived by post this morning i.e. very next day -well done Maplin, have just soldered one in place with only a faint hope of success, have fired it up and on broadcast band working right now. Now I suppose a long wire is called for.
I downloaded the circuit diagram and sharpened it with a photo editing tool, I am really grateful for the help I have received on here. I was a bit puzzled by the valve heater voltages 3 of them( 12BE6,12BA6 and 12AV6 are 12.6V and the 50C5 is up to 50V, but they are of course all 0.15A. It was an interesting exercise comparing all the component values with the circuit diagram, the only discrepancy I found was C7 - mine is clearly labelled 0.005 microfarad. The rectifier diode on the power side is identified as an S2C. As suggested on here the chassis appears to be isolated by capacitor from the mains input but I don't risk sticking fingers in regardless. I used to get a few jolts when I was a lot younger. The radio is on a local am station and even receiving old signals from 1960 -Buddy Holly-"Every day" |
12th Jun 2010, 10:54 am | #23 |
Dekatron
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Re: Lafayette HE-40 receiver
Excellent-better than your "recycling" plan anyway. Is their any chance you can post the new improved circuit diagram I wonder? Dave W
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12th Jun 2010, 11:02 am | #24 |
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Re: Lafayette HE-40 receiver
Hopefully this is it - Dave - http://i67.photobucket.com/albums/h3...-40circuit.jpg
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12th Jun 2010, 11:03 am | #25 |
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Re: Lafayette HE-40 receiver
Moderators -If I'm not allowed to post that please smack my hand!
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12th Jun 2010, 11:12 am | #26 |
Dekatron
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Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
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Re: Lafayette HE-40 receiver
That's really good William-thanks very much. I'm sure the Mods will have no problem. Might even inspire me to pull my sets out and poke around. I was amused to see the 12AV6 described on the comprehensive National Valve Museum site as one of the "magic three" 3AV6 3.15v 6AV6 6.3v and the 12AV6 at 12.6v as you say ...all derived from the same 6AT6 root apparently! Plenty of choice there I think.
Cheers Dave W Can't recall exactly what Patrick did re the PSU but he put some sort of regulator inplace that stabilised the HT and seemed to improve SW no end! Last edited by dave walsh; 12th Jun 2010 at 11:23 am. Reason: addition |
13th Jun 2010, 8:38 pm | #27 |
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Re: Lafayette HE-40 receiver
Talking about the valve museum - in the box (original) with the set were three valve boxes, one Mullard HBC91 priced at 10/6 which looks to be the equivalent/substitute for the 12VA6, a plain white box containing a 12BE6, no makers name apparent, pencilled price 16/- and an empty Brimar box for a
12BA6 which was stickered at 0.75p+VAT. The Mullard valve still has the BVA guarantee for 3 months on the condition that the purchaser had paid the full list price! |
1st Dec 2010, 4:00 am | #28 |
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Re: Lafayette HE-40 receiver
I have a HE-40 that i am working on for my son. Is there a replacement for the sr-12 or will a silicon diode with a higher piv work?
de KD4WOV Tom |
1st Dec 2010, 11:30 am | #29 |
Rest in Peace
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Re: Lafayette HE-40 receiver
Is the SR-12 a selenium rectifier? If so, you can replace it with a silicon diode with appropriate PIV, with a wirewound resistor in series (to mimic the drop of the selenium rectifier).
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3rd Dec 2010, 6:42 pm | #30 |
Rest in Peace
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Re: Lafayette HE-40 receiver
I think you'll find that the Heathkit model GR-91 is very similar - if not identical (except for the 'cosmetic engineering' ):
http://www.heathkit-museum.com/ham/hvmgr-91.shtml Al. [Skywave] |
13th Dec 2010, 6:40 pm | #31 |
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Re: Lafayette HE-40 receiver
Hi. I'm new to the forum.
I have an HE-40, which was working. Turned it on yesterday, and after it powered up, stopped receiving anything. Good hum from the speaker, but touching the grid of the 50C5 does not produce any more hum (which it should do i think). Anode and screen grid voltages on the 50C5 are both about 110V, from the spec sheet that's about right. Anode voltage on the 12AV6 is only about 50volts, though. I suspect the 50C5 is not working (it gets VERY hot)... Could anyone pls confirm the 12AV6 anode voltage (the triode's anode to be precise) on a working set? Thanks Roger |
13th Dec 2010, 7:30 pm | #32 |
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Re: Lafayette HE-40 receiver
You state that you have the voltages for the 50C5 'from the spec. sheet'. Presumably, this is the sheet for the receiver in question. So I now have to ask: does this spec. sheet specify 50v for the anode of the 12AV6?
The 50C5 will run hot: as a rough rule of thumb, if the anode isn't glowing red (!) then it's probably about right. Measure the voltage at its cathode - this will be the valve's bias and check that there is no positive voltage on the control grid. If there is, then the capacitor that connects to it from the anode of the 12AV6 is suspect. Check the value of the anode load resistor of the 12AV6: +/- 20% of its nominal value is acceptable. If all of those points check out OK, try placing your finger on the grid of the 12AV6. You should get a loud hum from the speaker. If still unsuccessful at isolating the fault at this point - and bearing in mind what you said about its apparent 'now not working' symptom - I'd now start thinking about a defective 50C5 or possibly the 12AV6, valve substitution being the best test. You may have insulation failure, heater-cathode, in the 50C5. Al. [Skywave] |
13th Dec 2010, 10:10 pm | #33 |
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Re: Lafayette HE-40 receiver
Thanks for that. I'll try your checks tomorrow evening.
The spec sheet is not from the receiver, it's from the BRIMAR data sheet for the 50C5, 'Typical operating conditions'. I know valves run hot, but this one is 'really' hot...makes me suspicious. Anyway, thanks for the quick response, and I'll let you know how I get on. Roger |
13th Dec 2010, 10:36 pm | #34 |
Nonode
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Re: Lafayette HE-40 receiver
DO NOT put your finger on the grid of the 12AV6. This is an AC/DC set and as far as I can see from the posts the 240Volt version uses an auto transformer. We still effectively have a live chassis.
Al
__________________
I won't tell you how I discovered that. |
13th Dec 2010, 10:44 pm | #35 |
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Re: Lafayette HE-40 receiver
OK, I would probably use a probe via a .01uF cap anyway!
Roger |
14th Dec 2010, 11:47 am | #36 |
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Re: Lafayette HE-40 receiver
Alistair - the reason I mentioned 'touch the grid of the 12AV6 with your finger' was simply because Roger (G3YTN) had already done that with the 50C5. Bearing in mind the measurements that he has made, it seems highly likely that he has already touched the metal chassis on more than one occasion.
Nevertheless, I know what you are thinking and your warning is appropriate: we have not yet conclusively established that the neutral side of the incoming mains supply is connected to chassis via the isolating R & C (R16 & C12 I think: here, the drawing is a little out of focus). Roger seems aware of the potential hazard anyway: he refers to using a probe plus a 0.01 uF capacitor. Al. Last edited by Skywave; 14th Dec 2010 at 11:51 am. Reason: Add comment, re the R & C isolating components. |
1st Jan 2011, 8:59 am | #37 |
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Re: Lafayette HE-40 receiver
Happy New Year to everyone.
Having got past Christmas, i found the problem - a loose connection near the BFO potentiometer. So now I can work on the alignment etc. Thanks to all of you for your help. 73 Roger |