Silvertone Stereo on the Fritz

Hi everyone, I'm back again concerning my Silvertone Model 3025 AM/FM Stereo Receiver I had gotten from Mr. Biggles for helping him out with his Voice of Music Console restore project. Anyways, I had gotten it recapped and retubed and up and up and running again and then for some reason or another it has all of the sudden lost the left channel and lost nearly 50% of its volume output capability, and I'm not sure why either. I had checked all of the tubes that I had installed in the stereo and they all checked out good on my tube tester.
My biggest concern is that I might have somehow lost my left channel output transformer but not sure how that could of happened because I never ran the thing without speakers attached and I never did anything that would of caused the output transformers to be strained beyond their limits.

Any ideas as to what might of happeded?

Also the reason why I said its lost nearly half (50%) of it volume output capability is because just to even hear anything the volume has to be turned up more than half volume to even hear anything.

Any help would be appreciated.

check the first preamp tube first. We need to know what the voltages are and find out if something got dropped. It's more than likely an open resistor/small cap in the preamp circuit.

Also check the diodes. I lost 25% of the volume on one channel of my Packard Bell which traced back to a bad/weak 5U4GB.The tube had gotten to the point where it supplying maybe 3/4 of the total voltage it was supposed to.

Hey captain, Have you gone through and checked the voltages according to the schematic?

I deleted the schematic you gave me so I can't remember if it had the voltages but I believe it did.

Does it do it on all inputs? AM, FM, AUX, phono?

cademan said:

Hey captain, Have you gone through and checked the voltages according to the schematic?

I deleted the schematic you gave me so I can't remember if it had the voltages but I believe it did.

Does it do it on all inputs? AM, FM, AUX, phono?

Click to expand...

yes it does do it on all of the inputs, it starts out fine for a few seconds after initial warmup but then after about 5 seconds it then loses half the volume, gets really distorted sounded and then I lose the left channel. I haven't checked any of the other voltages or anything else in there. I checked all the tubes and none of the tubes tested bad. maybe a bad coupling cap or two that I don't know about? it does have ceramic disc coupling caps which I know rarely fail, but there are some exceptions.

Artcurus said:

check the first preamp tube first. We need to know what the voltages are and find out if something got dropped. It's more than likely an open resistor/small cap in the preamp circuit.

Also check the diodes. I lost 25% of the volume on one channel of my Packard Bell which traced back to a bad/weak 5U4GB.The tube had gotten to the point where it supplying maybe 3/4 of the total voltage it was supposed to.

Click to expand...

it uses silicone diodes for rectification, it doesn't use a rectifier tube. I've tried it with a known NOS 12AX7 preamp tube and it still does it so its not the preamp tube but it definitely could be something in the preamp or amp circuit somewhere like a coupling cap or a bad resistor.

cademan said:

Hey captain, Have you gone through and checked the voltages according to the schematic?

I deleted the schematic you gave me so I can't remember if it had the voltages but I believe it did.

Does it do it on all inputs? AM, FM, AUX, phono?

Click to expand...

Cademen, tubes have been to known to fail after warmup. They test okay but after they get hot, they lose performance.

This really does sound like a tube is failing after initial startup or an open cap/resistor somewhere.

Artcurus said:

Cademen, tubes have been to known to fail after warmup.

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YUP! Already knew that! :yes:

Even if the tube(s) fail after warm up, voltages will still go down making it a dead give away.

Sometimes voltages will go up if there is a bad resistor. Especially around the preamp tubes.

Time to get a new pair of output tubes (or used from other equipment).

cademan said:

YUP! Already knew that! :yes:

Even if the tube(s) fail after warm up, voltages will still go down making it a dead give away.

Sometimes voltages will go up if there is a bad resistor. Especially around the preamp tubes.

Time to get a new pair of output tubes (or used from other equipment).

Click to expand...

Agreed.

cademan said:

YUP! Already knew that! :yes:

Even if the tube(s) fail after warm up, voltages will still go down making it a dead give away.

Sometimes voltages will go up if there is a bad resistor. Especially around the preamp tubes.

Time to get a new pair of output tubes (or used from other equipment).

Click to expand...

I'll have to double check the schematics I have for it on my computer and maybe I'll send the scematics your way again so you can take a look and see what might be the cause of the left channel failure, also when I swapped in the output tubes I had (including an old Telefunken EL84 from an old Grundig) they seemed to work fine same for the preamp tubes that I have that I swapped in and out.could it be possible for the tubes to not get the right voltages in the circuit and still be good?

captainclock said:

I'll have to double check the schematics I have for it on my computer and maybe I'll send the scematics your way again so you can take a look and see what might be the cause of the left channel failure, also when I swapped in the output tubes I had (including an old Telefunken EL84 from an old Grundig) they seemed to work fine same for the preamp tubes that I have that I swapped in and out.could it be possible for the tubes to not get the right voltages in the circuit and still be good?

Click to expand...

While *some* voltages variances are okay, the plate voltages on my PB can vary as much as 15 volts (notice this on the output tubes) depending on what kind of mood the line voltage coming in is in, MAJOR voltage swings are a problem and can really affect operation.

I have that schematic on a different drive, I'll see if I can find it later this afternoon.

Artcurus said:

While *some* voltages variances are okay, the plate voltages on my PB can vary as much as 15 volts (notice this on the output tubes) depending on what kind of mood the line voltage coming in is in, MAJOR voltage swings are a problem and can really affect operation.

I have that schematic on a different drive, I'll see if I can find it later this afternoon.

Click to expand...

Well my parents house which is what I was running it in after I got it running initially had a new 200 Amp breaker box installed a few years ago I really don't know what the line voltages are running into the outlets are in their house but I know at my place is around 125 volts AC ±5 volts and when I was running it it was acting like it was maybe getting too little voltage on the output and preamp tubes because I noticed that their filiments weren't glowing as brightly as the other tubes were. Would too little voltage on the tubes cause my problems?

Swap the right channel output tubes to the left channel and vice versa. See if the volume issue follows them. If it does, there's your problem. If not, swap the other tubes, one by one. Give it 15 minutes of downtime between power up/power off sessions, and make sure it's off for a minute before you pull tubes out.

EastPoint said:

Swap the right channel output tubes to the left channel and vice versa. See if the volume issue follows them. If it does, there's your problem. If not, swap the other tubes, one by one. Give it 15 minutes of downtime between power up/power off sessions, and make sure it's off for a minute before you pull tubes out.

Click to expand...

Alrighty, I actually did do something like that where I swapped the tubes out for one another and the audio issue didn't follow the tubes the non-working left channel issue stayed with the left channel no matter what tubes you stuck in there, and the low volume issues also didn't travel with the tubes it also existed no matter what tubes I used, which is why it kind of concerns me. :sigh:

Ok so I figured out what was causing my problem with the low volume issue, it was the same problem I had before, which was that pesky 2.2k ohm 1 watt resistor attached acoss the 2 47 MFD 350 Volt power supply caps for some reason this stereo doesn't like any of the 2.2k Ohm 1 watt resistors I give it, it just smokes them like Cuban Cigars and then they're done for. I'm not sure why its doing that but it is and I need to figure out a way to get it to stop smoking through and killing resistors. Any suggestions? Also I noticed that when I replaced the bad resistor with a known good resistor the volume for the audio went back to normal but I still have no audio in the left channel.... I was looking at the output tube sockets and they both have a small ceramic disc coupling cap going across pins 7 and 9 and the capacitors look like they're slightly burnt (they are discolored) could that be the reason why I don't have any audio in the left channel and why my stereo is burning through resistors?