41-250 No sound, glowing 41 tube, can't be a good thing - Printable Version
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+--- Thread: 41-250 No sound, glowing 41 tube, can't be a good thing (/showthread.php?tid=979)
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41-250 No sound, glowing 41 tube, can't be a good thing - justlrnin - 02-19-2008
Just finished re-capping my 41-250. Turned it on and got no sound except for a faint power supply hum from the speaker. I know I have a lot of trouble shooting ahead of me, but I noticed that the 41 tube closest to the edge of the chassis was glowing much brighter than the other. I switched the tubes and got the same result from the same socket. Is this normal? You can see the center element (heater?) glowing red all the way down to the base. The tube in the other socket is only has a faint glow at the tip of the center element.
- Harlan - 02-19-2008
Hi,
I'm new here and don't have a schematic or much help but it would sound like you maybe have an improper connection somewhere and if it only happend after "recapping" , is it possible you mistakenly relocated a wire on connection?
I guess I would measure the filiment voltage across the normal tube and compare with the other one. Seems like the filiment voltage is too high and may burn out your tube very soon if left this way. Trace the wiring to the filiment pins and check to see that it only has wires to it the same way as the good tube.
Also you may even have a short between pins or wire crossed somewhere causing this condition on the tube socket.
Hopefully someone else more familiar can help you a lot more... just throwing in my "2 cents" ha... best regards.
Harlan
- planigan - 02-20-2008
Hi justlrnin. Before you go any further have you run voltage readings per the schematic? Tubes can appear different because of their physical make up. I'm not saying you don't have a problem but you can only determine that by voltage checks. PL
PS: Before the voltage tests, did you do resistance checks on the various components, particularly the primary of the output transformer?
- justlrnin - 02-20-2008
Good call, Planigan. The output transformer tests open (it looks like garbage is growing in it). As for the filament voltage--it is right where it should be at 6.3v. I'll look for a replacement transformer (any suggestions where to buy one?) and move on to the next issue from there.
Thanks.
- planigan - 02-20-2008
justlrnin, glad you found it. As to the replacement I am not that conversant with that aspect. Has to be center tapped primary for push pull output. There is a parts supplier who has a collection of all kinds of parts for old radios but the name won't come to me. I have a note that vintage-electronics.com has philco parts. The other one may be oldradioparts-no something 'of the past'. Hopefully someone will chime in and help a fella with oldtimers. PL
- Terry Judkins - 02-20-2008
The Hammond HX-125H is a good choice. http://www.radiodaze.com/
- planigan - 02-20-2008
oldradioparts.com knew I'd get it! PL
- Ron Ramirez - 02-20-2008
PL - you're thinking of Play Things Of Past.
Justlrnin - I really think you should follow Terry's advice and use the new Hammond unit if you want your radio to be reliable in the long term.
- justlrnin - 02-20-2008
I placed my order tonight. Thanks to all for all the information and advice. I'm sure I'll be needing more assistance in the future. One other odd thing I found is that the multisection e-cap that I replaced was a 20mfd-20mfd. The schematic shows an 8mfd-16mfd. Would the 20-20 have had a negative effect the radio's performance?
- Ron Ramirez - 02-20-2008
No, as long as the working voltage of the condenser is the same or higher as the original, it will be fine.
- justlrnin - 02-27-2008
Here's an update on my 41-250--I installed the new Hammond transformer. I'm now getting sound from the speaker, but it's an oscillating sound from one of the output (41) tubes--the one that is glowing hotter than the other. Starting at the power supply I've run value tests and everything checks out okay until I get to the other side of the field coil. I'm getting a somewhat high 309v DC out of the rectifier (84), which then goes directly to the field coil where it comes out at 265v, but should be 180v according to the schematic. Of course this 265v gets passed through the new output transformer and to both output tubes. I checked the resistance of the field coil--1100 ohms dead on. I've checked many times all of the cap connections and everything is as it should be. Could the excessive voltage be a caused by a bad rectifier?
- rghines1 - 02-27-2008
Hi,
Based on the field winding reading you are only pulling 40 mA which is about half as much than normal. The 41 output tubes may be biased near cutoff. Check the grid bias is on the 41 output tubes. Didn't see a voltage mentioned in the Rider schematic but would expect it to be minus 15-20 volts. If much higher than this than perhaps resistor (part 61) may have an open section.
The 84 rectifier should be OK.
Richard
- justlrnin - 02-27-2008
She's singing again! (and I'm an idiot!
) Thanks, Richard, for pointing me in the right direction. When I started checking the grid bias on the 41s, I found that I had connected one lead of the output transformer primary to the grid pin instead of the anode (one pin off). The radio sounds great (what a rich sound) on all bands, except SW is picking up some static from the furnace blower motor. Pushbuttons work as well. I feel fortunate I didn't destroy something. I'm sure I took a few years of life out of the output tubes.Thanks, again, for everyone's help. My next project will be 46-350 with a blown up multi-cap. That should be interesting.
Bob
- Doug K. - 02-27-2008
Hey Bob, I just got done with a 48-360 similar to your 46-350. Nice sounding radio. I did a restuff on the multi-cap, not much room on that chassis. I unfortunately had 2 bad sections in the candohm so I had to mount 10 watt resistors on terminal strips outside the chassis- no room at all to mount them under that speaker!
- rghines1 - 02-27-2008
Hi Bob,
Congrats! That didn't take long and love those happy endings!
Richard