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 Post subject: Gloritone 99A Low Volume
PostPosted: Sep Fri 24, 2021 12:35 pm 
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Location: Hudson, MA 01749
I am restoring a 1931 Gloritone 99A cathedral-style radio. I've replaced all the capacitors and a few of the resistors, aligned the L.O, I.F., tested the tubes, etc. It works, however the volume is low, even at maximum volume setting. I know this radio has a different type of volume control circuit compared to other radios; that is, the "volume" control is actually in the RF section and appears to control the strength of the incoming signal as well as alter the behavior of the autodyne circuit. I removed and examined the potentiometer; it measured 5.6K ohm and the wiper pin appeared to track across that range, although with intermittent gaps in connectivity. I replaced it with a new 10K Ohm potentiometer (assuming that was okay since the schematic indicated an 8K pot). The volume control behavior is a little better (not crackly as with the original pot). However the volume level at maximum setting is still rather low. I was expecting to hear room-filling sound. Do these sort of radios typically not have loud audio output?


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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Fri 24, 2021 1:02 pm 
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ab1aw wrote:
I am restoring a 1931 Gloritone 99A cathedral-style radio. I've replaced all the capacitors and a few of the resistors, aligned the L.O, I.F., tested the tubes, etc. It works, however the volume is low, even at maximum volume setting.
I don't know what to expect from this radio nor what you are getting, but If I was in that situation I would check the plate voltages ("B" Volts) and Screen voltages of each tube. See if there is any major issue with any of them (particularly the audio output). Variations of 20% should not cause significant loss of signal.
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Curtis Eickerman

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Fri 24, 2021 1:58 pm 
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Total agreement with Curtis. Check volts first & if B+ is high that's a clue. Do pay attention to the cathode volts. That can tell you if a tube is working properly. A weak tube e.g. mixer can reduce output. There are many variables here, even the antenna is implicated.

Do check your work, sometimes the wrong part creeps in. Your problem best handled step, by step. The set is relying on RF return via the power transformer & that can be an issue. As noted many times we tend here, to ground the chassis on sets like that. Beware of "M", that in this set is 1000; that has lead to wrong resistor fitment.

Do make sure the Signal Generator is on frequency and the right one (instructions on data sheet)? Setting with a Frequency Counter has traps. Keep the Generator input down & ensure there is DC blocking (Cap) between it and the mixer grid. I normally use around 100pF with them. As there is no AGC and even on sets with it, there is such a thing as too much signal, & it swamps it.

It was normal in the early Autodyne (Screen grid) radios to have the volume controlled by increasing the self bias on the mixer and often first IF.

If you are not sure: Do ask before doing it.

Marcc


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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Fri 24, 2021 3:50 pm 
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Location: Hudson, MA 01749
Thank you both for this assistance and guidance.

I measured those pins and observed these voltages. They are all way off (except for the filament voltages). I suspect there is some common fault affecting all the tubes? I'll need to look at those power supply resistors that are in that metal bar (can't remember the name of that thing).

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Fri 24, 2021 4:53 pm 
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Where did you connect the negative lead of your voltmeter? Try using the cathode (filament of 47) of each tube as the negative point and see if your voltages are closer to what is in the table.

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Fri 24, 2021 6:47 pm 
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Location: Hudson, MA 01749
Curtis, Eric, Marc,

Thank you all for the comments. I rechecked the components and found another bad resistor; the 3,000 Ohm grid bias on the first 224 was way out of spec (1,200 Ohm). Replaced that and then rechecked the voltages. I also noted that I needed to check voltage with the volume control at full maximum (not minimum). This gave me some better measurement results (see below). I also made the measurements relative to ground for the first set below, and relative to the tube's cathode for the second set (except for the cathode measurement itself). That gave me better grid measurements for the first 3 tubes.

In any case, the radio is blasting now. Sounds really good and picking up the local stations I expect.

Now on to restoring the cabinet.

Thank you all very much!

Mike

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sat 25, 2021 1:24 am 
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All good; love an easy fix.

In most cases, and it should be either in the text, or on the schematic, as to what type of meter was used and what the reference is. That is the Zero volts point which is normally chassis. In this case info is on the voltage chart.

Also note the significant comment on the 300 Ohm resistor. You will note that the centre tap of the set, goes to ground Via it. The voltage drop across it forms part of the tube bias, normally that of the output tube and any error in the voltage across it outside accepted variations (20%) is indicative of a fault like a dead tube.

Sets like this that do not play ball, are for your education. Do note that a Digital Meter will give higher voltage readings with bigger resistors due to less circuit loading.

Marcc


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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sat 25, 2021 4:26 am 
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A radio like that needs a realy long antenna ,to play loud and do some stations play a lot louder than others .

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sat 25, 2021 4:47 am 
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It is good the set is working but it still seems the voltages are high. The voltages in the table from Curtis are directly from a US R&T manual via Riders, I recognize the format. Earlier this year I restored a 12 tube US R&T set from 1932-33. The service manual for my radio indicated the voltages in the table were taken with a 1,000 Ω/Volt meter, using the highest range consistent with getting a good reading. As noted, line voltage is 115 volts, not sure what your line voltage line was.
Based on the terminology of “socket voltage” and “B volts” it indicated to me the voltages were taken at the tube socket and not to a common negative point. These sets were only a few years removed from when radios did have A, B and C batteries. When I finished mine up, I created two voltage tables both using a VTVM, one table with the negative lead to the chassis and the other table at each socket. They voltages between my two tables are not even close. However, the table I created measuring from the cathode at each tube is very close to the table in the service manual. The Candohm resistors can be a trouble point, but not always all the ones in my set were still good as well as the dogbones.

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sat 25, 2021 12:24 pm 
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I note from the data that this set does quote tuning using the volt meter method. Many meters of the time had a specific plug for that and I have more than one radio here where the set had a dedicated plug for that method. "Peak" 200H was one such meter. Should you have a meter like that it has likely got a 0.1uF cap in series with that plug & like 200H and several others it will by now be a dud & leak like a sieve. With that method the voltage is taken from the plate of the output tube and read on a low AC Range.

Those voltages quoted & supplied by Curtis are not, (as I see it) measured with a 1000 ohm per meter. The reference on the chart suggest it may have been a VTVM. What looks like 600,000 suggests: Not analogue.

If the line voltage goes high, that will invariably cause a rise in B+ but will also cause a rise in back bias voltage as the current increases through the 300 Ohm resistor.


http://www.nostalgiaair.org/pagesbymode ... 043782.pdf

Marcc


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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sat 25, 2021 2:33 pm 
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Not trying to start a back and forth about the voltage, however the only item that was measured specifically with a 600,000 Ω/V meter is note (2), screen grid of the 224 second detector. A 1,000 Ω/V with a 600-volt scale would meet the requirement. The Riders does not have the full text of the service manual, I am getting my information from the text of the full-service manual for a US R&T radio of the same timeframe which is more specific.
At the end of the day once the radio is operating properly a new voltage table can be made using more modern equipment and documenting the conditions. Still miss the Breakfast Club from ABC, I used to listen to it every day when I got home from work.

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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sat 25, 2021 3:33 pm 
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I do have a range of meters from them gravitating here. Its criminal was has happened to some, destroying them. A precision Signetics being destroyed by batteries being one. I shudder to think of the dollars paid for it.

The joy of keeping & sorting the good ones, leaves a better opportunity to check questionable things with an analogue meter "of the time". RCA on various occasions, pointed out that the voltage being measured was not the actual voltage the Radiotron was working at. That is why one appreciates those suppling references listing the meter spec. as well as the voltages: Many don't.

Marcc


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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sun 26, 2021 11:27 am 
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Location: Hudson, MA 01749
Marcc wrote:
The set is relying on RF return via the power transformer & that can be an issue. As noted many times we tend here, to ground the chassis on sets like that.
Marcc

I did notice the grounding the chassis reduces the volume significantly. That was unexpected.


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 Post subject: Re: Gloritone 99A Low Volume
PostPosted: Sep Sun 26, 2021 11:56 am 
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That does sound odd, make sure the antenna wires have not been tampered with inside the set. There may be an earth leakage problem with the transformer; If it is excessive a GFCI should trip out.

You might have to tweak the antenna coils trimmer?

Marcc


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