23-04-2017, 08:04 AM
I think the 47 ohm given for R11 is an error.
Lawrence.
Lawrence.
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Soviet East German Radio
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23-04-2017, 12:39 PM
I couldn't find C30's value. Maybe we should take R11 for 47 K and standardise. Have you noticed HT supply to the LO windings via a switch. When I return to radio work all of this must be traced. For now, I am tiling the shower-room.
Don't forget the Kid Jenson show on Signal 2 medium wave today at about 17.40 - he plays seventies and eighties charts and great music.
23-04-2017, 12:53 PM
Yes, it's an error. Radio Museum shows the ECH81 with the customary 47 K. That helps clear it up.
05-06-2017, 12:42 PM
(This post was last modified: 05-06-2017, 12:48 PM by Nowhere-Man.)
Something I noticed. The EABC80 triple diode triode in my schematic seems to show 3 cathodes. The schematic is of continental standard so the cathode is typically shown as a big black dot. This EABC80 is used in the ratio detector circuit and is shown split or segmented. Looking at the pin layout below I wasn't sure what s K T means. One of the diodes here has its own cathode. Also I wondered about C 51. Is the "a" just clarifying anode?
I thought it was strange to ground out detector anodes although I have an Ultra where this was done to the AVG anode. Anyway 3 black dots is odd because there should be two. I may be wrong here but I think the Foster Seeley ratio detectors used just anodes for conversion whereas a cathode was used in other detectors (anode and cathode)
05-06-2017, 01:29 PM
KT is the triode cathode, "a" and "c" at C51 are the connection test points for a meter circuit when aligning FM.
Lawrence.
05-06-2017, 03:14 PM
This what led me to assume two cathodes:
"The EABC80 is a triple diode triode. The triode and two diodes share a common cathode but one diode has a separate cathode." http://www.r-type.org/exhib/aaa0405.htm So, to me, the way it was worded above is every electrode has one cathode in common but a diode has a cathode of its own. So, that set me to wondering. Added to that, 3 cathodes seems unusual. Yet the schematic shows 3 black dots and the black dots in this case indicate a cathode.
05-06-2017, 03:22 PM
Also C51 seemed to come to a dead end. This ought to be by my reckoning the AM audio frequency derived from the ratio discriminator. There does seem to be a switching system but anyway logic dictates the AF here must be switched into the final output stage. At this point I don't have the schematic on hand so a bit hard to explain what I mean.
What they should have said is that two of the cathodes share a common connection, there's three cathodes in the valve, each one heated by its own heater, the three separate heaters are series connected in the valve.
Two of the cathodes have to share a common connection because there are only 9 pins available in total for all the electrodes and heaters. The way the valve is graphically represented in the Philips valve data sheet sums it all up. The audio output is via the tertiery winding and R20/R22. Lawrence.
05-06-2017, 04:05 PM
(05-06-2017, 03:24 PM)pwdrive Wrote: What they should have said is that two of the cathodes share a common connection, there's three cathodes in the valve, each one heated by its own heater, the three separate heaters are series connected in the valve. O.K. thanks. I just accessed the schematic online. I was relying on memory so confusing matters. L23, L24 and L25 is where we're at in the discriminator circuit. R20 and R22 I can see. I think I'd meant C44 so will finish off tonight. The link is here as a refresher for anyone who wants to see the circuit. You can see there the 3 cathodes. Any comments on the FM circuit welcome - it uses variometers. vorkreisvariometer was a word I had some difficulty finding even on line at the time. Pardon the earlier confusion over the capacitor. http://85.144.220.212/nvhr/RFT_5170.pdf |
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