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Post by frank1956 on Mon Jun 30, 2014 3:51 pm

Hey you guys have been busy I see. Can I do anything while I wait on the filter cap? Thanks again to all of you for this help, I sure do appreciate it.

Oh by the way I have both digital and analog meter's. I tried both and the digital does not stay on any one reading for very long, so I can get an accurate reading/measurement.
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Post by 75X11 on Mon Jun 30, 2014 4:17 pm

Wildcat445 wrote:That's a good plan, 75.  The primary of the OT should be okay, witness B+ on the plate of the 50L6.  A short from primary to secondary was not something I considered.  Good idea!

WC

That got me thinking. If you have B+ on the plate of the 50L6, there couldn't be any short between the pri & sec of the output xfmr. the ground on the secondary would take it out. So, maybe a move further back might be in order.
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Post by Wildcat445 on Mon Jun 30, 2014 4:37 pm

Frank, you may find my comment here rather unusual, since I am a proponent of analog meters for old radio work, BUT, in THIS case, a PROPERLY calibrated and zeroed digital meter will be what is required to figure out where we need to be.  Apparently the resistance (impedence) of the speaker and output transformer is so small that all you really "see" on your analog meter is zero ohms.  This is due to paralax error, the difference your eye sees between the needle being right on the mark, or perhaps slightly to one side of the mark or the other.  Is this totally confusing?  A digital meter is accurate to tenths of an ohm, and that is what we are going to have to see before we can be 100% sure of where we are.  Did you read the post above, about using a battery to see if your speaker works?  That is the next thing to try.  The radio should be off and unplugged for this test.

Get a battery preferably a C or D cell, but those are not common anymore.  a 1 1/2 volt battery would be safer to use than a 9-volt.  In any case, you take jumper leads and connect one jumper lead to the negative (-) end of the battery and the other to the positive (+) end.  You hook the jumper wire from the negative end of the battery to one terminal on the speaker, then just touch the positive end jumper lead to the other terminal on the speaker.  If the speaker is working, you will hear a click in the speaker.  No click equals a dead speaker.  Did you sub the speaker to see what effect that had?

(I edited and deleted this paragraph, since 75 and I were posting at the same time, and my comments here would have been confusing. Sorry, 75)

Let us know what you find.  You can do this while you are waiting on your parts, if you'd like.  Thanks, Tom, for your research on the resistance on the OT and speaker on an actual working radio.

WC

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Post by Wildcat445 on Mon Jun 30, 2014 4:53 pm

Let's do a click test on the speaker, then move on. If the speaker is good, there has likely been a mis-step that we have not caught that has given us a false indication of some kind. We will move on to the front end, like you suggested.

WC

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Post by 35Z5 on Mon Jun 30, 2014 5:14 pm

The transformer on my similar Silvertone  is .5 ohm secondary, 185 ohm blue to red & 12.7 ohm red to yellow... It plays very good and will pin a 2W audio meter when cranked up...

If the secondary winding isn't referenced to ground, could be leakage between primary & secondary and radio still play play... Of course can't say I remember any small OPT having this condition, generally the primary is open when xfomer has failed...
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Post by frank1956 on Mon Jun 30, 2014 6:13 pm

Battery test checks out OK. Speaker made a loud click when battery positive lead was touched to speaker lead.

No I have not sub the speaker out.
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Post by Wildcat445 on Mon Jun 30, 2014 6:30 pm

That's great, Frank. That proves that the speaker is okay, and that our problem with the Output transformer is one of being able to measure small resistance. Tom has pretty much laid that concern to rest with his research into one of his radios. Our next foray will be into the front end of the radio, from the volume control back to the antenna. If Tom or 75 want to make a suggestion where to start, they can get you started. We need to make sure we are not losing our signal in the IF stage first. We can assume at this point that the audio section is working, and that your test from the volume control was not effective. Everything checks out, so the audio section should work. We have certainly checked everything. Not being thorough is not our problem. Congratulations, Frank. You have officially checked out your radio from the plug on the cord, to the volume control, to the speaker, "leaving no stone unturned." Good job.

While you are waiting for parts, we will get our heads together and figure out the plan of attack.

WC

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Post by 75X11 on Mon Jun 30, 2014 7:26 pm

I would suggest making certain of the tube voltages starting from the antenna forward and determine if any readings would be off enough to account for the fault.
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Post by 35Z5 on Mon Jun 30, 2014 7:30 pm

75X11 wrote:I would suggest making certain of the tube voltages starting from the antenna forward and determine if any readings would be off enough to account for the fault.

Agreed, if there is no plate(pin 7) voltage on the 12AV6, the volume control test won't work... Should be 50v...
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Post by Wildcat445 on Tue Jul 01, 2014 1:07 am

I have been making notes on the schematic as we went along, and I have noted that the plate voltages on every tube has been checked.  Did I write something down wrong?  I have 57 volts written by the side of the tube symbol.  B+ has been running a few volts high all along.  I agree that plate voltage on the 12AV6 should be verified. None of the other elements have been checked, according to my notes.

WC

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Post by frank1956 on Tue Jul 01, 2014 12:34 pm

WC I do not remember checking the plate voltage on 12AV6. Can this been done without the filter cap I am waiting on?
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Post by 35Z5 on Tue Jul 01, 2014 1:15 pm

Yeah voltage will prob be low but still there... Might just be a good test, should hum missing a filter cap...
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Post by frank1956 on Tue Jul 01, 2014 4:38 pm

Checked voltage on tube 12AV6 pin #7 without filter cap. Measured between 14-15 volts.
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Post by 35Z5 on Tue Jul 01, 2014 5:19 pm

Well that's quite a bit lower than I would expect, but I suppose we should wait for the cap & measure again before condemning the couplate... Are you sure the tubes are in the correct sockets???

Does the radio hum without the cap???

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Post by frank1956 on Tue Jul 01, 2014 5:29 pm

Yes tubes are in the correct sockets, and the radio did hum without filter cap.
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Post by Wildcat445 on Tue Jul 01, 2014 11:42 pm

It appears to me that B+ to the 12AV6 comes from the same cap as the screen voltage for the 50L6. Would not low screen voltage on pin 4 of the 50L6, clear the couplet of suspicion? The voltage on the screen was okay, a bit high, when we were working there.

WC

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Post by 35Z5 on Wed Jul 02, 2014 12:48 am

Wildcat445 wrote:It appears to me that B+ to the 12AV6 comes from the same cap as the screen voltage for the 50L6.  Would not low screen voltage on pin 4 of the 50L6, clear the couplet of suspicion?  The voltage on the screen was okay, a bit high, when we were working there.  

WC

Probably, if there is over 100v on 50L6 screen and only 15v on 12AV6 plate the couplet defiantly is suspect... I even had recheck the 50L6 screen voltage typed out and then changed my mind, as we won't really know till the cap is replaced... Tubes can react in odd ways with AC on the elements...
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Post by Wildcat445 on Wed Jul 02, 2014 11:31 am

I have all kinds of marks and notes on the schematic. Where I got the reading for the 12AV6 is anybody's guess. Old age, maybe.

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Post by frank1956 on Wed Jul 02, 2014 6:51 pm

I am back online. Filter cap re-connected. Measurements taken from 12AV6 pin #7 are between 22-23 volts
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Post by 35Z5 on Wed Jul 02, 2014 7:23 pm

Umm that is only approx half what it should be, but the 12AV6 will function with only 15-20v on the plate... If pin 4 on 50L6 is still at over 100v, there surely is a issue with the couplate(this assumes the 12AV6 isn't shorted)... Biggest issue is they are not avail unless you find a used one and requires eight parts to replace it...

BTW I once had a radio that played and 12AV6 plate was at 11v, all components were good... Turned out the 12AV6 was a rebrand(Shield from Olson Electronics) and wasn't a 12AV6 at all but a 12AE6 intended for car radio usage, normally operates with four or five volts on the plate... Yes it was marked 12AV6 but wasn't orig to tube...
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Post by frank1956 on Wed Jul 02, 2014 10:39 pm

Pin #4 on tube 50L6 is still between 112-113 volts.
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Post by frank1956 on Wed Jul 02, 2014 10:47 pm

35Z5 wrote:Umm that is only approx half what it should be, but the 12AV6 will function with only 15-20v on the plate... If pin 4 on 50L6 is still at over 100v, there surely is a issue with the couplate(this assumes the 12AV6 isn't shorted)... Biggest issue is they are not avail unless you find a used one and requires eight parts to replace it...

BTW I once had a radio that played and 12AV6 plate was at 11v, all components were good... Turned out the 12AV6 was a rebrand(Shield from Olson Electronics) and wasn't a 12AV6 at all but a 12AE6 intended for car radio usage, normally operates with four or five volts on the plate... Yes it was marked 12AV6 but wasn't orig to tube...


So is that good news or bad news for me?????
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Post by 35Z5 on Wed Jul 02, 2014 11:09 pm

Possibly bad, though there may be a work around...

With set unplugged, measure between pins 6 & 7 of the couplate.. Should be 470,000 ohms, meter needs to be set to Rx 100K scale...

While you're at it measure voltage on pins 5 & 6 of 12BA6 & 12BE6, should be same as pin 4 on 50L6... Also measure pin 5 of 50L6, should be near zero volts...
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Post by frank1956 on Wed Jul 02, 2014 11:21 pm

Pin # 5 & 6 on tube's 12BA6 & 12BE6 measure between 114-115 volts all away around. Pin 5 on 50L6 is zero.

Not sure what sure pins 6 & 7 of the couplate is???
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Post by 35Z5 on Wed Jul 02, 2014 11:51 pm

Mustard colored disc that has seven leads coming from it... Pins will be numbered...
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