Replacing parts indiscriminately is not really a method, it's more like Russian roulette except if you get it right you are lucky instead of unlucky.
Can you post a picture of the amp wiring?
Here is what we know so far: The power supply and rectifier (6CA4) tube appear to be working fine, as well as the tuner. The amp section tubes are the 6CG7 (driver tubes) and the 6BQ5's (output tubes). Is there a single 6BQ5 for each channel?
Have you confirmed that the amp tubes filaments are good? ie, do all of the tubes glow in dim light when the unit is on?
Have you swapped tubes, one at a time, from one channel to the other? If the problem follows a tube, then you have a place to start from. You only need to swap the 6CG7's and the 6BQ5's, those are your amp tubes.
These tests are simple, and do not require any test equipment. If the heaters are all glowing, and the problem does not follow a tube, then you'll probably need to start checking some voltages.
Do you have a multimeter with clip leads? You'll need clip leads instead of probes for your safety.
There is one other basic test that does not require any test equipment and checks for bad solder joints and other connection problems and that is to wiggle each component while the amp is turned on to check for bad solder joints and other wiring issues. You need to use a non-conductive poker/probe to do this without zapping yourself, such as a wooden stick, etc. Keep in mind that there are lethal voltages (300-400 VDC) powering the tubes and you need to respect this.
Finally, there is the possiblity that the signal wiring for the left channel is grounded/shorted to earth somewhere. That would also cause little to no sound output. check to make sure that the input wires as well as the wires to the speakers are not touching the chassis anywhere, look for worn wire insulation, etc.
Can you post a picture of the amp wiring?
Here is what we know so far: The power supply and rectifier (6CA4) tube appear to be working fine, as well as the tuner. The amp section tubes are the 6CG7 (driver tubes) and the 6BQ5's (output tubes). Is there a single 6BQ5 for each channel?
Have you confirmed that the amp tubes filaments are good? ie, do all of the tubes glow in dim light when the unit is on?
Have you swapped tubes, one at a time, from one channel to the other? If the problem follows a tube, then you have a place to start from. You only need to swap the 6CG7's and the 6BQ5's, those are your amp tubes.
These tests are simple, and do not require any test equipment. If the heaters are all glowing, and the problem does not follow a tube, then you'll probably need to start checking some voltages.
Do you have a multimeter with clip leads? You'll need clip leads instead of probes for your safety.
There is one other basic test that does not require any test equipment and checks for bad solder joints and other connection problems and that is to wiggle each component while the amp is turned on to check for bad solder joints and other wiring issues. You need to use a non-conductive poker/probe to do this without zapping yourself, such as a wooden stick, etc. Keep in mind that there are lethal voltages (300-400 VDC) powering the tubes and you need to respect this.
Finally, there is the possiblity that the signal wiring for the left channel is grounded/shorted to earth somewhere. That would also cause little to no sound output. check to make sure that the input wires as well as the wires to the speakers are not touching the chassis anywhere, look for worn wire insulation, etc.
boywonder said:
Yes is not good practice to radomly replace parts. However, the caps would have needed replacing anyways. I will borrow a digital camera to take a very good picture of the underbelly of this amplifier chasis. When I applyed power and the right channel was going strong and the left dead, all the tubes lit up and were glowing.
There appeared to be seperate tubes (both of the same nunber) for each of the two channels, I did swap them and there was no change. I am puzzled, because this amp is not complicated at all really! There can only be so many ways for the amp section to have a failed left channel.
I was in your position 1996 when 60's tube amp fell into my lap and I decided to restore it. I knew basic electrical theory and I could do maths, but hadn't really done electronics before except a few kits that I had built but never understood. Thanks to helpful people on the net I step by step got the picture what the circuit was doing and managed to get it right. In the end I probably replaced every single component, something I wouldn't do today as I think some circuits have a sonic signature that it is good to preserve if possible. I'll try to share some of my experiences.
First, get the schematic. If you can't find it for that exact model, there is a very high probability that other models in the lineup shared the same basic configuration. Back then I actually got the whole service manual for my Philips from the company itself, at no cost! They were just glad I wanted to keep their old stuff running.
Even if you are not experienced with scematics now, you will be after this
- Make lots of notes. And take it slowly, no need to rush things when there are dangerous voltages involved.
Duncanamps.com has a database of tube pinouts, very useful. Study schematics of other radios and amps that uses the same tubes, to get an idea of what to expect.
Some say not to take the "shotgun" approach, replacing blindly. I would say the opposite when it comes to capacitors. They are all bad or will be very soon. If a cap that is supposed to couple the signal voltage but block DC between stages is leaky, you might fry any new tubes you put there. Same goes for possibly shorted cathode bypass caps. Nowadays I sometimes replace those on an old set before even plugging it in. So I think you should figure out the values of all the small caps, and buy modern replacements.
Polypropylene or polyester types rated for 630 volts for coupling anodes to grids, and just common small electrolytics of the right value/voltage between cathodes and ground - if you can't see what the cap was marked as, just try 50uf rated for 50v for the cathodes and it should produce sound without blowing up. Electrolytics have + and - like batteries, look carefully.
The big power supply capacitor cans are working, or they would have exploded by now, but replace those too later.
The multimeter is your "eye". You have no idea what is going on until you measure. As one channel is working, I would take measurements of the voltages between the tube pins and chassis ground, make notes and compare the channels. Small variations of +/- 10 percent are of no significance, but if one anode pin has +280v and the same pin in the other channel +50v, then you know that something is wrong.
Forget about the oscilloscope for now. It is an even better "eye" showing where the signal goes, but for basic troubleshooting it is fine to use a cheap digital multimeter set to the high or medium DC voltage scales. One clipped to ground, other clip on the pin to measure, after that turn the amp on and wait half a minute for the voltages to stabilize. That is the safest way even if it is time consuming. Make sure the clip has insulated handles and doesn't tough anything else.
If nothing helps, in the end you have some very nice parts to build a new single-ended amplifier with: The power and output transformers, two 6BQ5 power tubes, and the 6CG7 drivers. These are all you need for a basic good sounding small amp. There are a tons of schematics on the net to choose from.
Sorry for the long post, hope it did some good. Now I'm off to town.
First, get the schematic. If you can't find it for that exact model, there is a very high probability that other models in the lineup shared the same basic configuration. Back then I actually got the whole service manual for my Philips from the company itself, at no cost! They were just glad I wanted to keep their old stuff running.
Even if you are not experienced with scematics now, you will be after this
- Make lots of notes. And take it slowly, no need to rush things when there are dangerous voltages involved.Duncanamps.com has a database of tube pinouts, very useful. Study schematics of other radios and amps that uses the same tubes, to get an idea of what to expect.
Some say not to take the "shotgun" approach, replacing blindly. I would say the opposite when it comes to capacitors. They are all bad or will be very soon. If a cap that is supposed to couple the signal voltage but block DC between stages is leaky, you might fry any new tubes you put there. Same goes for possibly shorted cathode bypass caps. Nowadays I sometimes replace those on an old set before even plugging it in. So I think you should figure out the values of all the small caps, and buy modern replacements.
Polypropylene or polyester types rated for 630 volts for coupling anodes to grids, and just common small electrolytics of the right value/voltage between cathodes and ground - if you can't see what the cap was marked as, just try 50uf rated for 50v for the cathodes and it should produce sound without blowing up. Electrolytics have + and - like batteries, look carefully.
The big power supply capacitor cans are working, or they would have exploded by now, but replace those too later.
The multimeter is your "eye". You have no idea what is going on until you measure. As one channel is working, I would take measurements of the voltages between the tube pins and chassis ground, make notes and compare the channels. Small variations of +/- 10 percent are of no significance, but if one anode pin has +280v and the same pin in the other channel +50v, then you know that something is wrong.
Forget about the oscilloscope for now. It is an even better "eye" showing where the signal goes, but for basic troubleshooting it is fine to use a cheap digital multimeter set to the high or medium DC voltage scales. One clipped to ground, other clip on the pin to measure, after that turn the amp on and wait half a minute for the voltages to stabilize. That is the safest way even if it is time consuming. Make sure the clip has insulated handles and doesn't tough anything else.
If nothing helps, in the end you have some very nice parts to build a new single-ended amplifier with: The power and output transformers, two 6BQ5 power tubes, and the 6CG7 drivers. These are all you need for a basic good sounding small amp. There are a tons of schematics on the net to choose from.
Sorry for the long post, hope it did some good. Now I'm off to town.
I have only built 3 amplifiers from scratch, but I have repaired many. So lets go about it in a very simple manner.
Question 1 - do all the amplification tubes light up when you turn it on?
- Check both sections of the tubes - there should be a 2 heaters in each amplification tube. Both should be orange. If you have no heater you get no sound.
Question 2 - Follow the wiring from the speakers back to the amplification circuit. Is the wiring intact? check it with an ohmeter. Get yourself an inexpensive digital multimeter if you don't already have one.
Question 3 - If the Speaker wiring is intact have you tried switching channels? (maybe your left speaker is no good).
Question 4 - Is there any extra fuses in the circuit (besides the mains fuse)? These could be high voltage fuses, and one may be blown. - Note: if it is blown then there is probably a reason!
It is also possible that a coupling capacitor is open circuit. These are often radial capacitors with paper housing in old equipment. They will read something like 0.22MFD 400V or similar on the side. If they are in a paper casing then they tend to dry out and die after 35+ years. If they are metal then open circuit is also possible. If they are not paper or metal, but plastic (ie. orange drop) then this is unlikely.
There are a lot of possibilities. These are just some ones that come to mind since you said there was no sound at all.
In any case it is very bad practice to plug in an old unused tube amp.. If you really want to do that then at least get a variac and bring it up slowly (over many hours).
Please be careful with High voltage capacitors! they still hold a big charge after you turn it off! You will want to drain them before doing work! You can use a 5 watt or bigger 300 ohm resistor to drain the + end to ground. Don't short them to ground with a wire! Use a voltmeter (red lead to + and black lead to -) to check that they have no charge!
Please read the sticky on safety all the way through and ask questions if you are not 100% sure.
Question 1 - do all the amplification tubes light up when you turn it on?
- Check both sections of the tubes - there should be a 2 heaters in each amplification tube. Both should be orange. If you have no heater you get no sound.
Question 2 - Follow the wiring from the speakers back to the amplification circuit. Is the wiring intact? check it with an ohmeter. Get yourself an inexpensive digital multimeter if you don't already have one.
Question 3 - If the Speaker wiring is intact have you tried switching channels? (maybe your left speaker is no good).
Question 4 - Is there any extra fuses in the circuit (besides the mains fuse)? These could be high voltage fuses, and one may be blown. - Note: if it is blown then there is probably a reason!
It is also possible that a coupling capacitor is open circuit. These are often radial capacitors with paper housing in old equipment. They will read something like 0.22MFD 400V or similar on the side. If they are in a paper casing then they tend to dry out and die after 35+ years. If they are metal then open circuit is also possible. If they are not paper or metal, but plastic (ie. orange drop) then this is unlikely.
There are a lot of possibilities. These are just some ones that come to mind since you said there was no sound at all.
In any case it is very bad practice to plug in an old unused tube amp.. If you really want to do that then at least get a variac and bring it up slowly (over many hours).
Please be careful with High voltage capacitors! they still hold a big charge after you turn it off! You will want to drain them before doing work! You can use a 5 watt or bigger 300 ohm resistor to drain the + end to ground. Don't short them to ground with a wire! Use a voltmeter (red lead to + and black lead to -) to check that they have no charge!
Please read the sticky on safety all the way through and ask questions if you are not 100% sure.
I am at a loss, trying to find information, ANY information on this RCA Victor console! I can't even get a picture!
I punched in the numbers I saw on the back panel and I got no leads.
It says:
RCA 1040714-23
This is printed on a sticker that shows where such and such tube goes in what socket.
I punched in the numbers I saw on the back panel and I got no leads.
It says:
RCA 1040714-23
This is printed on a sticker that shows where such and such tube goes in what socket.
rknize said:
Pa-ha-ha! I know I realized this later! But there IS a small sticker
all by itself that says the model number, but the first few letters have been torned off. Because the paper is so brittle. I punched in the numbers that remained, because most of them were there but I got no information out of google.
The numbers that remained are: SHC668
Half the first letter is ripped though, but I think it is an S
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.