TV front Deluxe from 1950 - loss of sustain

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Drewbertca
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Re: TV front Deluxe from 1950 - loss of sustain

Post by Drewbertca » Tue Feb 13, 2018 5:05 pm

For tubes. Canadian outfit. Good to deal with.http://www.thetubestore.com/Search?go=&search=6sc7

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oid
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Re: TV front Deluxe from 1950 - loss of sustain

Post by oid » Fri Feb 16, 2018 4:38 pm

This is likely a tube issue, resistors and caps generally do not wait 20 minutes to start causing problems. Either way a visit to a tech is in order, the power supply caps should be replaced, they sometimes fail as a short and fry expensive parts of the amp, also the coupling caps are likely leaky and many of those carbon comp resistors drifted far from value, these are likely the reason the amp distorts so easily. Despite popular belief these amps do have clean headroom when working at spec. I would have to take a gander at the schematic but if memory serves the tv front should have simular headroom to the tweeds, perhaps abit more, I do not recall what sort ofphase inverter is in these or the power tube bias, so hard to say off of memory, perhaps after work I will check the schematic.

Also, 3 prong is a must, there is good reason it is illegal to make amps with live chassis these days, if you life is important to you, get a properly installed grounded chord on that amp.

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Re: TV front Deluxe from 1950 - loss of sustain

Post by Guitarman555 » Sun Feb 18, 2018 8:51 am

oid wrote:
Fri Feb 16, 2018 4:38 pm
This is likely a tube issue, resistors and caps generally do not wait 20 minutes to start causing problems. Either way a visit to a tech is in order, the power supply caps should be replaced, they sometimes fail as a short and fry expensive parts of the amp, also the coupling caps are likely leaky and many of those carbon comp resistors drifted far from value, these are likely the reason the amp distorts so easily. Despite popular belief these amps do have clean headroom when working at spec. I would have to take a gander at the schematic but if memory serves the tv front should have simular headroom to the tweeds, perhaps abit more, I do not recall what sort ofphase inverter is in these or the power tube bias, so hard to say off of memory, perhaps after work I will check the schematic.

Also, 3 prong is a must, there is good reason it is illegal to make amps with live chassis these days, if you life is important to you, get a properly installed grounded chord on that amp.
Oid, many many thaks for your reply, I will definetely go to a tech. But before, I would like to lookt the amp little bit, I am curious, maybe some easy parts I could do with my dad who has repaired many electronics devices, including amps. But doesn t have experience with guitar amps. If you could look in to the schematics and tell me excatly what to change, we would be able to do it here without any problem. Many thanks!

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Re: TV front Deluxe from 1950 - loss of sustain

Post by oid » Sun Feb 18, 2018 1:45 pm

There is no way to know what parts need to be replaced without having the amp on the bench so it can be tested under working conditions, it may need little replaced, it may need to be gutted and rebuilt. Paying the money for reputable tech to fix it up will only increase the value of the amp and help insure it is still working in another 70 years. This is a task that is within the ability of most anyone, but you will need to learn some basic theory, mainly Ohms law and the basic operation of vacuum tube amplifiers, how to use a meter and learning point to point work.

The basic rundown of the process would be to take the schematic and compare it to the amp, confirm if it is accurate and figure out if any discrepancies are original to the amp or later modifications. Once that is done you need to check supply voltages and bias voltages while the amp is working into a dummy load, Fender tended not to put these values on schematics back then, so you need to get out the tube data sheets and calculate what the bias should be. Resistor values should also be checked at this point, the value of an old resistor can be very different under operating conditions then when cold, the previous measurements would let you know which resistors are worth checking, but in such an amp they pretty much should all be checked. Next power off, pull the tubes and fire it back up to check if the coupling caps are leaking. Once you have done this you will have a fairly good idea of what needs to be done.

Here is a good rundown of how a tube amplifies if you want to go for it, gives a suitable base to build on.
http://www.aikenamps.com/images/Documents/ampfund.pdf
Going through the first pages here, probably everything up through "Ohm's Law" is a good idea as well.
http://www.aikenamps.com/index.php/white-papers
That will get you 90% of the way there to understanding your amp and to a point where you will be able to ask reasonable questions, assuming you spend the time to understand and comprehend what you read!

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Re: TV front Deluxe from 1950 - loss of sustain

Post by Guitarman555 » Sun Feb 18, 2018 2:19 pm

oid wrote:
Sun Feb 18, 2018 1:45 pm
There is no way to know what parts need to be replaced without having the amp on the bench so it can be tested under working conditions, it may need little replaced, it may need to be gutted and rebuilt. Paying the money for reputable tech to fix it up will only increase the value of the amp and help insure it is still working in another 70 years. This is a task that is within the ability of most anyone, but you will need to learn some basic theory, mainly Ohms law and the basic operation of vacuum tube amplifiers, how to use a meter and learning point to point work.

The basic rundown of the process would be to take the schematic and compare it to the amp, confirm if it is accurate and figure out if any discrepancies are original to the amp or later modifications. Once that is done you need to check supply voltages and bias voltages while the amp is working into a dummy load, Fender tended not to put these values on schematics back then, so you need to get out the tube data sheets and calculate what the bias should be. Resistor values should also be checked at this point, the value of an old resistor can be very different under operating conditions then when cold, the previous measurements would let you know which resistors are worth checking, but in such an amp they pretty much should all be checked. Next power off, pull the tubes and fire it back up to check if the coupling caps are leaking. Once you have done this you will have a fairly good idea of what needs to be done.

Here is a good rundown of how a tube amplifies if you want to go for it, gives a suitable base to build on.
http://www.aikenamps.com/images/Documents/ampfund.pdf
Going through the first pages here, probably everything up through "Ohm's Law" is a good idea as well.
http://www.aikenamps.com/index.php/white-papers
That will get you 90% of the way there to understanding your amp and to a point where you will be able to ask reasonable questions, assuming you spend the time to understand and comprehend what you read!
Hi Oid, many thanks once again. I will go through that. Meanwhile I changed 2x6v6 tubes and the sustain problem is over! Also distorting amp at too low volumes is over. It keeps clean up to 3 from 12 , which is already pretty loud clean tone possible go through with a band with drummer, which I find reasonable. But one problems is still there - again after cca 20minutes the amp gets distorted already from 1or2 on volume. I will try to change also the rest of tubes. Do you think those could be the 2 small preamp tubes (6SC7) or the rectifier(5Y3 GT)?

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Re: TV front Deluxe from 1950 - loss of sustain

Post by oid » Sun Feb 18, 2018 2:50 pm

If the volume control has no effect on the distortion and just turns the volume down, it is the first gain, so the outer 6SC7, you can try swapping it with the other 6SC7 and see what happens. The first gain stage of this amp is grid leak biased and they can be picky and cause various issues with tired old tubes, even if it fixes the problem it will not rule out other problems which you are unaware of and it may just make new problems.

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Re: TV front Deluxe from 1950 - loss of sustain

Post by Guitarman555 » Mon Feb 19, 2018 3:37 am

oid wrote:
Sun Feb 18, 2018 2:50 pm
If the volume control has no effect on the distortion and just turns the volume down, it is the first gain, so the outer 6SC7, you can try swapping it with the other 6SC7 and see what happens. The first gain stage of this amp is grid leak biased and they can be picky and cause various issues with tired old tubes, even if it fixes the problem it will not rule out other problems which you are unaware of and it may just make new problems.
You did not understand, volume control does have impact:
First 20 minutes - Tone is clean up to number 3
After 20 minutes - Tone starts to breakup very soon, cca number 1. But still more volume you do, more distorted tone is

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Re: TV front Deluxe from 1950 - loss of sustain

Post by Guitarman555 » Mon Feb 19, 2018 3:38 am

Guitarman555 wrote:
Mon Feb 19, 2018 3:37 am
oid wrote:
Sun Feb 18, 2018 2:50 pm
If the volume control has no effect on the distortion and just turns the volume down, it is the first gain, so the outer 6SC7, you can try swapping it with the other 6SC7 and see what happens. The first gain stage of this amp is grid leak biased and they can be picky and cause various issues with tired old tubes, even if it fixes the problem it will not rule out other problems which you are unaware of and it may just make new problems.
You did not understand, volume control does have impact:
First 20 minutes - Tone is clean up to number 3
After 20 minutes - Tone starts to breakup very soon, cca number 1. But still more volume you do, more distorted tone is
Are 6SC7 interchangable with 12AX7? I dont think so, but only to coublecheck

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Re: TV front Deluxe from 1950 - loss of sustain

Post by mgeek » Tue Feb 27, 2018 8:21 am

There's a fair chance you could fry any valves you switch in if it's 'something else'. Been there done that, and it's not worth the risk imo.

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Re: TV front Deluxe from 1950 - loss of sustain

Post by oid » Tue Feb 27, 2018 1:36 pm

"fair chance" is a bit extreme, perhaps "off chance." Swapping a dead tube without checking why it popped can fry a tube, this is why you keep a tired old tube about, pop it in before you put the brand new one in, if it promptly dies, take the amp to the tech, if not pop in the new one and forget about it. In this case we are talking about swapping two working tubes, so we are moving that "off chance" into the odds of hititng the jackpot in the lottery.

In the case of preamp tubes there is little risk, but if you can justify the expense of taking an amp to a tech for tube changes, then that is a good thing, especially if you have a good tech who checks your fluids and tire pressure why he is at it.

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Re: TV front Deluxe from 1950 - loss of sustain

Post by Guitarman555 » Mon Mar 26, 2018 7:01 am

oid wrote:
Tue Feb 27, 2018 1:36 pm
"fair chance" is a bit extreme, perhaps "off chance." Swapping a dead tube without checking why it popped can fry a tube, this is why you keep a tired old tube about, pop it in before you put the brand new one in, if it promptly dies, take the amp to the tech, if not pop in the new one and forget about it. In this case we are talking about swapping two working tubes, so we are moving that "off chance" into the odds of hititng the jackpot in the lottery.

In the case of preamp tubes there is little risk, but if you can justify the expense of taking an amp to a tech for tube changes, then that is a good thing, especially if you have a good tech who checks your fluids and tire pressure why he is at it.
Hey, so you would advice to change 2 small preamp tubes (6SC7) or the rectifier(5Y3 GT)? Thanks

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Re: TV front Deluxe from 1950 - loss of sustain

Post by oid » Mon Mar 26, 2018 1:10 pm

Guitarman555 wrote:
Mon Mar 26, 2018 7:01 am
Hey, so you would advice to change 2 small preamp tubes (6SC7) or the rectifier(5Y3 GT)? Thanks
I said you can try swapping the two preamp tubes with each other, move preamp tube 1 to preamp tube 2's spot and vise versa, if there is a drastic change in sound, then you know you have an ailing preamp tube(s). This will not solve any underlying problems, which an amp of this age almost certainly has, and can, and often does, lead to more or worse problems in the long term. Band-aide fixes such as replacing tubes on a sick old amp are fine for getting you through a gig, but will likely just cause headaches if they are used for any amount of time.

Avoiding what maybe $20 in parts and a hours bench time with a tech may very well turn into many hundreds of dollars in parts alone. I would not recommend this path you seem to be so fixed on following. As I keep saying, either learn to fix it properly or take it to someone who knows how to do so.

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