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Help with Bosch 48 - Printable Version

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Help with Bosch 48 - daveone23 - 07-12-2024

Well i finally finished recapping the Bosch48 but its pulling way too much current, like 146watts. Somethings i know:
1. Transformer is putting out correct filament voltages
2. Resistance on 80 rectifier plates is 160ohms, 80ohms each side to ground.
3. 80 rectifier filament pins measure .1ohm
4. When 80 tube is pulled watts are 40.
5. All filter caps replaced are non polarized polys.

Anything i can try to verify if the transformer is good and also locate the source of the draw

RE: Help with Bosch 48 - morzh - 07-12-2024

With the 80 pulled, are all other tubes in?
They will very well through filaments amount to 40W.

With all the tubes in, and the speaker connected you will have the draw on the order of 100W.
Pull push-pull output tubes, see if your power drops and how much.

Your power transformer is likely OK, else you would not have that power draw only with the 80 in.

Also see the voltages, if they reasonably matched with the expected ones, corrected for whatever meter you use (a modern DMM will show higher values).

RE: Help with Bosch 48 - daveone23 - 07-12-2024

Yes, when I pulled the 80 tube I left the rest of the tubes in to get 40watts. The 80 rectifier is getting way too hot. What should the B+ be at C21 and L7? Are you sure about the 100 watts, seems like alot.

RE: Help with Bosch 48 - morzh - 07-12-2024

Well, the filaments of all tubes plus pilot, without the 80, draw 24W.
I am not counting the centertap resistors.
I do not know what the efficiency of the power transformer is. Or what the initial losses that occur just from plugging it in without load.
You have 16W going somewhere. Does the transformer get too warm over time without load, if you just plug it and run without tubes?
You said your filament voltages are good, which is a good sign; how about the Hi-V rectifier - it is supposed to be around over 600V end-to-end.

The tubes (with 80 in) dissipation should be around 17W.
The rectifier is another 10W in filament power, plus the dissipation (plate resistance times the full rectifier current, which I do not know).
L7 will drop some significant power.
L6 will also drop some.

The radio, which is comparable to Philco 20, should be about 75W total.


Remove all tubes, so transformer has no load, and see what it draws and whether or not it gets hot.



PS. Check the biases (when tubes are in) against the tables. See if any tube runs too hot. The 80 is always very hot when loaded.
Measure voltages across the tube; especially across 80 (P to K).

PPS. Cannot see the field coil consumption, but in Philco 20 it is about 5W (125V at 3,100 ohms)

RE: Help with Bosch 48 - daveone23 - 07-12-2024

Here is some data I took:

1. #80 tube filament resistance 2.8K each side
2. watts: no tubes = 12 no#80=45 all tubes=135 without speaker choke
3. #80 plate voltage 752vac
4. 45 tube plates 198vdc
5. plates of 24 tubes - 300mv (something wrong here)
6. filaments 24s 2.8vac
7. C20 284vdc

RE: Help with Bosch 48 - morzh - 07-12-2024

Well, you need to find out why your 24 tubes have 0V at plates.

Is the 27 tube OK? (plate voltage).

What is this "outlet" in series with B+ voltage (going to 24s and 27 tubes)?
If it is open, the 24s will have their plates at 0V while your 45 tubes will be OK, which seems to be the case.

RE: Help with Bosch 48 - daveone23 - 07-12-2024

Yea, thats the field coil for the speaker. I disconnected it because the watts went to about 150. Thats why the 24
Plates dont register. Any other things i should look at?

RE: Help with Bosch 48 - morzh - 07-12-2024

Well, I would start going a load by load. Pull/measure.


Oh...forgot to ask: have you checked all the tubes?
And does the transformer get hot/too warm when no tubes are present?

RE: Help with Bosch 48 - daveone23 - 07-12-2024

Tested all tubes. The transformer is shielded. I would have to remove all the shielding.

RE: Help with Bosch 48 - morzh - 07-12-2024

No, don't remove shielding. A transformer that runs hot will warm up fast.
I am trying to exclude a turn short, though from the behavior it is not it.

Like I said, unless someone has specific experience with this specific radio and could point you directly to the source of trouble (I do not), I would start with bare transformer (no tubes) and go from there.

Now,


1. You seem to have the input voltage switch: has it been set correct?
2. Input capacitors: are they correct value? No, caps do not draw power.
3. BTW, how do you measure your power? Kill-a-Watt or Ammeter/V-meter?

RE: Help with Bosch 48 - daveone23 - 07-12-2024

Iam using the 118volt line value since my house voltage is around that. I think the other setting is 126.
Iam using a kilowatt meter. Radio is pulling 1.25amps.
The voltage divider resistors are getting roasting hot in a short time.

RE: Help with Bosch 48 - morzh - 07-12-2024

That could be one of the extra loads.
Measure voltage across it, measure the resistance, if it is sections, measure each section's resistance and each section's respective voltage drop. Do it for all hot dividers.
Then calculate the power (U-square over R).

I am riding to FL tomorrow, so I am packing the rest of the evening, and if I answer, it will be sporadic at best; maybe someone else will chime in. Tomorrow I will be riding the whole day and will not be here.

RE: Help with Bosch 48 - Chas - 07-12-2024

Dave,

I posted a reply to ARF a few minutes before I saw your post here...

I basically said the same, but I got a bit more obscure. Look for components like transformers leaking to chassis...

Chas

RE: Help with Bosch 48 - daveone23 - 07-12-2024

I pulled the 45s and got the watts down to 100watts

RE: Help with Bosch 48 - morzh - 07-12-2024

Have you measured the resistors?

Also, Chas has a good point.
But to measure leakage you need to disconnect the filter caps across the AC.