Vol control ? - Printable Version
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Vol control ? - Eric - 07-26-2015
I have an American Bosch 04 http://www.nostalgiaair.org/pagesbymodel/251/M0022251.pdf
the second print is the one.
The vol control is open and there is nothing on it besides I'm pretty sure it is not original. I have tried pots from 5k to 500k and all I get is a whisper out of it with it at max. I have about 25' of wire strung in my garage for an antenna. What am I missing? #7 is 48k and #5 is .1uf . Thanks
Eric
RE: Vol control ? - KCMike - 07-26-2015
Eric Have you changed the caps in it and tested all the tubes? If not that, I would check the antenna coil. I would also ck R7, C3 and C5 not saying its the problem but where I would start. Also did you do voltage checks on the tubes?
If I'm not close on my advise someone will see this and get you in right direction. Good luck.
RE: Vol control ? - Radioroslyn - 07-26-2015
Hi Eric,
The volume control is going to be a fairly low value as it is in the ant circuit. Probably 10K to 20k should be about right. As Mike said it important to replace the caps and then you can measure voltages to figure out what going on. Without replacing the cap you run the risk of burning up the power transformer which you don't want re replace. It special cause it has a 2.5v filament winding very hard to find.
If you have done the replacements measure the voltage on the plate of the 47. That would be on pin 2.
Terry
RE: Vol control ? - Eric - 07-26-2015
(07-26-2015, 06:21 PM)Radioroslyn Wrote: Hi Eric,
The volume control is going to be a fairly low value as it is in the ant circuit. Probably 10K to 20k should be about right. As Mike said it important to replace the caps and then you can measure voltages to figure out what going on. Without replacing the cap you run the risk of burning up the power transformer which you don't want re replace. It special cause it has a 2.5v filament winding very hard to find.
If you have done the replacements measure the voltage on the plate of the 47. That would be on pin 2.
Terry
Thanks guys,
Probably should have posted all I have done so here is what I have
All tubes tested and are good.
Re capped all.
I have replaced the resistors ( not that many and the dog bones were mostly way over)
2.5V filament ? The 25z5 and the 43 have 25 volt filaments. the ballast tube the 185R8 checks out also.
The voltages are as follows
screen plate cath Fil
25Z5 ---- 118 ----- 61
43 120 122 35 37
6c6 52 40 5 6.3
6d6 122 120 .6 12
Some are off not sure why. I have checked the RF coils and there good tomorrow I 'll do the ant.
RE: Vol control ? - Radioroslyn - 07-26-2015
Sorry I was looking at the 1st schematic, it has 2.5v tubes.
As you may know this is a TRF set consisting of a RF amp a detector, and audio out. The plus is it's pretty simple the down side is poor sensitivity.
The cathode voltage on the 43 seems a bit high but it does use a 600 ohm resistor in the cathode. Most I've seen are a bit lower around 300 ohms.
Double check your ant coil and then use a good ant read long and high up.
Terry
RE: Vol control ? - Eric - 07-28-2015
(07-26-2015, 08:51 PM)Radioroslyn Wrote: Sorry I was looking at the 1st schematic, it has 2.5v tubes.
As you may know this is a TRF set consisting of a RF amp a detector, and audio out. The plus is it's pretty simple the down side is poor sensitivity.
The cathode voltage on the 43 seems a bit high but it does use a 600 ohm resistor in the cathode. Most I've seen are a bit lower around 300 ohms.
Double check your ant coil and then use a good ant read long and high up.
Terry
Found my mistake it was on the 43 tube part 13,14,15 had these wired wrong. To be fair I started this radio when I first started the hobby ran into the dead end and put it on the shelf thinking I need to get more experience. The 5k pot works fine but I need to get one with a longer shaft, not a big deal!. thanks again for helping!
Eric
RE: Vol control ? - Radioroslyn - 07-28-2015
Glad to be of help. Depending on how long a shaft you need I've used a piece of 1/4" hose has a coupler to another shaft. If it slips use a tieraps to secure it.
Terry