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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Mon 13, 2020 1:14 am 
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Disconnected all leads to the Input Transformer and confirmed the numbers I got before re-installing it (1.148K, 5.65K, 8.4K) on the three windings. No sign of shorting to core, frame or between windings. Will continue to check connections as Chas suggested.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Mon 13, 2020 1:42 am 
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The detector grid to A+ circuit appears correct, the 6.6 megohm grid leak resistance.

At any time, when it was operating, was the regeneration control, (marked amplification), turned and was there an observable point were the set went into regeneration and out of?

If the set did not "squeal" at any time there is a problem in the detector. Still could be an amp problem too.. That is why I suggested going over the detector circuit, all of it with great care, including that wave change switch...

What is the status of the antenna and ground? Is a real EARTH ground in use and how far away is it?

Chas

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Mon 13, 2020 2:01 am 
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None of the tuning controls made any difference when I had the headphones plugged into the headphone jack. They all worked fine with the headphones patched in to posts 1 and 2 of the H transformer.

Antenna and ground are the same as always, 150 of wire in the attic and ground is a 14 gage wire clamped to a cold water pipe about 12 feet away. They have never been an issue with any of my radios.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Mon 13, 2020 4:20 am 
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atwaterkent1 wrote:
None of the tuning controls made any difference when I had the headphones plugged into the headphone jack. They all worked fine with the headphones patched in to posts 1 and 2 of the H transformer...


Tell me DID it SQUEAL?? At any time, when it was operating, was the regeneration control, (marked amplification), turned and was there an observable point were the set went into regeneration and out of?

If the set did not "squeal" at any time there is a problem in the detector. Still could be an amp problem too.. That is why I suggested going over the detector circuit, all of it with great care, including that wave change switch...

If it did squeal, antenna ground is good, signal at headphone when patched at 1-2, that says that the problem is in the amp. But could be just a dirty connections at the headphone jack. The jack must complete the circuit to the speaker driver, if is does then the driver could be bound with the diaphragm hitting the pole piece. The headphone jack may have poor connections when the headphone is plugged in.

Those are the beginning checks.

More if need be....

Test at the tube pin not the socket, partially extract the tube and slip the probe to the side of the tube pin.

To move on be sure there is grid voltage impressed on all three AF tubes. Grid voltage that is too high may be caused by an open connection. Grid voltage according to the schematic is impressed all the time, there is no current flow. The grid voltage cannot be measured if there is a failure when the radio is on as touching a grid with the probe will leak off high grid voltage and show the actual voltage. If you have a VTVM with a 10 meg or higher input resistance, that will show if a grid voltage has cut a tube off. Most DVMs are 1 meg, that would kill an impressed grid voltage. The obvious method to check if a grid circuit is open is to measure the resistance of the grid to C-, if those measurements are the same as the known transformer winding resistance. If these reading in your estimation are correct.

Excessively high impressed grid voltage will cut the tube off, no signal will pass or may pass intermittently even to the point of squealing or motor-boating.

Move to: Being sure the plates of the tubes have continuity via the transformers back to the B+ 90, resistance readings would be equivalent to the transformers resistance EXCEPT for the primary of transformer "K" which will be a parallel value based on the setting of the "P" switch.

If all these checks on the AF system are correct, then the only fault I can perceive is that there is a phase problem in the connections of the duplex windings used for phase splitting. It would be a trial and error issue of use of the AF generator and the scope to see the 180 phase shift if correct or no phase shift if wrong.

It is possible that both these transformers with duplex input/output windings could be wrong.

YMMV

Chas

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Mon 13, 2020 2:27 pm 
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atwaterkent1 wrote:
jrehkopf wrote:
OK, good deal. Jump the 2 C battery terminals with a good jumper wire. Measure resistance from 1st audio grid to A- terminal. Don’t tell me continuity, give me a number.



6.6M Ohms.

Huh? Should read resistance of the H transformer secondary, 1800 ohms. Bad connection or missing wire in that circuit. Connection from C+ to A- missing?

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Tue 14, 2020 5:25 pm 
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Dan, something else to try. Disconnect 2 on K transformer, connect phones to that wire and to 4. In addition, connect a jumper wire from H transformer terminal 3 directly to B-.
Attachment:
RGtemp.jpeg
RGtemp.jpeg [ 116.14 KiB | Viewed 512 times ]

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Wed 15, 2020 11:11 pm 
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jrehkopf wrote:
atwaterkent1 wrote:
jrehkopf wrote:
OK, good deal. Jump the 2 C battery terminals with a good jumper wire. Measure resistance from 1st audio grid to A- terminal. Don’t tell me continuity, give me a number.



6.6M Ohms.

Huh? Should read resistance of the H transformer secondary, 1800 ohms. Bad connection or missing wire in that circuit. Connection from C+ to A- missing?


Bad jumper, it just went into the trash. Checks 1.964K ohms.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Wed 15, 2020 11:40 pm 
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atwaterkent1 wrote:
Bad jumper, it just went into the trash. Checks 1.964K ohms.

Not the first time for a bad jumper. See the parts candy ad; buy the jumpers with the large clips.

If the H transformer secondary is 1800, where is the other 164 ohms coming from?

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Wed 15, 2020 11:48 pm 
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Different meters. Rechecked with Simpson that I used for previous check and it checks 1800 with it, so its a match.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Wed 15, 2020 11:49 pm 
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jrehkopf wrote:
Dan, something else to try. Disconnect 2 on K transformer, connect phones to that wire and to 4. In addition, connect a jumper wire from H transformer terminal 3 directly to B-.
Attachment:
RGtemp.jpeg


Getting nothing through headphones.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Thu 16, 2020 12:14 am 
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Chas - In one tube mode I can definitely get it to SQUEAL!

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Thu 16, 2020 4:58 pm 
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Well carp!
Something else to check. Connect all back like it should be, no power applied. Clip your ohmmeter to the input primary. There looks to be some sort of switch on that 5 section resistor. 6 positions? Rotate that switch from one end to the other; you should get 6 different readings on the meter. Guessing from high of about 1.15KΩ down to around 470Ω.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Fri 17, 2020 1:12 am 
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That 5 step resistor is the volume control and it checked out fine Jeff.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Fri 17, 2020 4:54 pm 
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I was curious as to the actual resistance readings at K primary terminals..

Can you measure the voltages at the actual tube pins? Connect all voltages, including the 3v C, then measure volts from A- to tube pins on 1st audio tube, plate and grid pins.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Sat 18, 2020 12:03 am 
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jrehkopf wrote:
I was curious as to the actual resistance readings at K primary terminals..

Can you measure the voltages at the actual tube pins? Connect all voltages, including the 3v C, then measure volts from A- to tube pins on 1st audio tube, plate and grid pins.


K transformer = PRI: 1.144K , SEC: 5.641K , TER: 8.44K


Plate - 96.1v
Grid - 48v

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Last edited by atwaterkent1 on Apr Sat 18, 2020 3:43 am, edited 3 times in total.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Sat 18, 2020 1:26 am 
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K transformer = PRI: 1.144K , SEC: 5.641K , TER: 8.44K <--- O.K. considering sec. #2 starts on top of sec. #1, has to have the same turns...

Plate - .006v <--------------- And the negative probe is where? Needs to be on B- should be 90 volts and if the "B" battery is inside the "B" is on all the time... The driver or 1st audio tube uses "K:" trans. in its circuits.

Grid - .008 v <--------------- And the negative probe is where? Needs to be on B- should be 3 volts and if the "C" battery is inside the "C" is on all the time... The driver or 1st audio tube uses "K" trans. in its circuits.

The step volume control simply shunts out the primary of "K" leaving all but 700 ohms so the transformer is not completely shorted.

It is necessary to provide point of references for the voltages and resistances given. IE Both probes. A reference back to some other post does not play, there are now 5 pages to look up what the SOP is. Similarly refreshing each page with a copy of the schematic is a big help

Chas

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Sat 18, 2020 3:39 am 
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I wriggled some wires when retesting because I was wondering about the voltage fluctuations, I've been removing and re-soldering some connections over and over again running different tests and found a couple that could have been better (nice way of saying I did a lousy job). I've corrected the numbers in my last post and there's no fluctuations now. I had the meter negative lead on the B- of the ARBE and then the A-, the voltages came out the same. Sorry about the mistake. :oops:

Voltages on the last two amp tubes didn't seem right, plate pin 96v and grid pin 3.98v (grid pin actually checked -3.98v until I reversed the leads, positive lead on the ARBE).

Chas- Here's the schematic you requested. It is a good idea to re-post on each page.

Attachment:
Radiola Grand Schematic.jpg
Radiola Grand Schematic.jpg [ 555.94 KiB | Viewed 456 times ]

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Sat 18, 2020 4:38 am 
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When taking voltage measurements that are not related to the "A" supply reference B-.

For this radio referencing the A- values will be influenced by the setting of the "N" filament rheostat.

Grid - 48v <--------------- And the negative probe is where? Needs to be on B- should be 3 volts and if the "C" battery is inside the "C" is on all the time... The driver or 1st audio tube uses "K" trans. in its circuits. This the first audio tube? At -48 volts bias this tube is effectively cut off no signal will be available for the primary of the "K" transformer. That is how it looks but I think this is another measurement error. If, indeed the grid is +48 volts there will be heavy plate current, the tube will be way out of its characteristic so no signal will pass through the "K" transformer. Again, measurement error or a wiring error at the "H" transformer... Operating a directly heated tube with excessive plate current can paralyze it, kill the emission, in oxide tubes, permanently ruin the tube. In thoriated tubes it is possible to rejuvenate...

Definitely review this measurement again. it should be -3 volts at the first audio grid measured from B-


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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Sat 18, 2020 3:43 pm 
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Quote:
Voltages on the last two amp tubes didn't seem right, plate pin 96v and grid pin 3.98v (grid pin actually checked -3.98v until I reversed the leads, positive lead on the ARBE).


Actually, these readings are exactly correct, 96 and minus 3.98. The first audio tube should read the same. Something is mis-wired or shorted to the 48 volt circuit.

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 Post subject: Re: Radiola Grande Restoration
PostPosted: Apr Sat 18, 2020 4:35 pm 
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I'll go through the 48v circuit.

Chas - My last post stated where the negative lead was connected, the ARBE B-.

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