Hi there
A friend asked if could take a look at his Fender PA100, now that I restored my old receiver successfully. I have never been inside an amp of this kind - only my old Pioneer receiver, so there are many things I don't know, but by now I can understand most of what is on a schematic (I have downloaded http://schems.com/manu/fender/pa100rev.pdf).
Also I have read that these amps aren't to fiddle with unless you know what you are doing. Well I hope I have enough sense to avoid the dangers, but if some caring person will point out what I should look out for I'd feel a whole lot more safe.
The story he (the owner) told me is, that he was playing his Gibson hooked into it, when he sensed the smell of smoke, the sound disappeared so he switched it off instantly. This happened about 3 years ago and it haven't been powered on since.
My plan is to open it up and look for obvious damaged components, and when I have peeked inside I will post my observations, in the hope that I can get some good advice.
Can there still be charge stored in it after 3 years, or can I safely put my fingers inside?
Maybe I should take some voltage readings just to be sure.
Thanks
Ole
A friend asked if could take a look at his Fender PA100, now that I restored my old receiver successfully. I have never been inside an amp of this kind - only my old Pioneer receiver, so there are many things I don't know, but by now I can understand most of what is on a schematic (I have downloaded http://schems.com/manu/fender/pa100rev.pdf).
Also I have read that these amps aren't to fiddle with unless you know what you are doing. Well I hope I have enough sense to avoid the dangers, but if some caring person will point out what I should look out for I'd feel a whole lot more safe.
The story he (the owner) told me is, that he was playing his Gibson hooked into it, when he sensed the smell of smoke, the sound disappeared so he switched it off instantly. This happened about 3 years ago and it haven't been powered on since.
My plan is to open it up and look for obvious damaged components, and when I have peeked inside I will post my observations, in the hope that I can get some good advice.
Can there still be charge stored in it after 3 years, or can I safely put my fingers inside?
Maybe I should take some voltage readings just to be sure.
Thanks
Ole
Last edited:
I would think unless powered up, you will be safe with this to take a look.
Please post the correct model number as Fender do not list a PA100 schematic. Thanks.
Please post the correct model number as Fender do not list a PA100 schematic. Thanks.
Last edited:
Always be safe and check for voltages, caps can store high voltage. Open her up and look for burnt resistors etc........
Use one of these Powering Up Your Radio Safely With a Dim-bulb Tester and fire her up watching V7-V10, if they red plate or the dim bulb grows bright shut her down. If the fuse doesn't blow and the dim bulb doesn't glow brightly check the voltages against the schematic.
Use one of these Powering Up Your Radio Safely With a Dim-bulb Tester and fire her up watching V7-V10, if they red plate or the dim bulb grows bright shut her down. If the fuse doesn't blow and the dim bulb doesn't glow brightly check the voltages against the schematic.
Attachments
Thanks, Jon, I will post more details later on - he will come by and drop it off saturday.
Wow. what a nice amp!
Check the capacitors for leaking and maybe it will be just a 6L6 that has gone down. Fingers crossed. If it is, change all four.
Fender don't go back that far apparently!
Check this out https://www.youtube.com/watch?v=nswcAPvH0P8
Check the capacitors for leaking and maybe it will be just a 6L6 that has gone down. Fingers crossed. If it is, change all four.
Fender don't go back that far apparently!
Check this out https://www.youtube.com/watch?v=nswcAPvH0P8
If its of any age the electrolytics will need changing.
I would also check coupling capacitors for leakage as any leakage could make the valves red plate.
Other than that I would disconnect the power supply for the amp and power it up to check voltages. This will eliminate a power supply fault.
I would also check coupling capacitors for leakage as any leakage could make the valves red plate.
Other than that I would disconnect the power supply for the amp and power it up to check voltages. This will eliminate a power supply fault.
Thanks, 'bird. I'll check for voltages even it's 3 years since it was powered on, then, no reason to run the risk.
I made a DBT to my receiver restoration project, so that is at hand.
Can you please spell out what "red plate" means 😕 - that expression is new to me - but I guess it could mean 'hot'?
Red plating is when the anode glows red due to too much current flowing.
This is often caused by a duff coupling capacitor or the bias being wrong.
On one of my designs I accidentally left out a grid stopper resistor when constructing the amp and the anode glowed bright red.
This is often caused by a duff coupling capacitor or the bias being wrong.
On one of my designs I accidentally left out a grid stopper resistor when constructing the amp and the anode glowed bright red.
Last edited:
Yep, check for leaks.
What a nice video from the Fender factory - pure charm and nostalgia 🙂
Can hardly wait to the weekend to get my hands on (and in) this amp and have a closer look.
Old worn out power tubes can draw excessive current and red plate..........hopefully just a fresh quad of 6L6GC's and you'll be up and running.
You can test this by removing opposite pairs of valves and powering it up.
I did this with an old Simms-Watts 100 watt valve amp.
I even ran it for a while with 2 valves removed until the new valves arrived.
Thanks, Nigel.
That's exactly what I was thinking - it should be from around 1980 - I would say that qualifies for being aged 😉
I have have seen the term 'coupling capacitors' time and again, but I never understood what specifies this/them and how to determine where/what they are on the schematic - perhaps you can help me on this?
I like your suggestion regarding disconnecting the power supply, and check it, good point - I didn't think of that!
The coupling capacitors AC couple the signal between stages.
It stops the DC getting through but allows AC through.
If these fail you can get many DC volts going to the grid and the valve opens right up and red plates.
There seems to be sevaral different 6L6's in Thomans shop:
6L6 Vacuum Tubes - Thomann UK
any particular version that is more correct among these?
edit:
Ahh, I see now on the schematic that it says '6L6GC', which is listed at Thomans...
6L6 Vacuum Tubes - Thomann UK
any particular version that is more correct among these?
edit:
Ahh, I see now on the schematic that it says '6L6GC', which is listed at Thomans...
Last edited:
Cross my fingers to that
But wouldn't you also agree that it's old enough (35 years) to replace the caps?
Last edited:
The electrolytic capacitors probably yes the amp could benefit from fresh caps but if they are not completely defective (within tolerance and functioning) it isn't necessary to replace them.
I would only replace blocking/coupling caps if they were leaky/defective.
If you have faulty 6L6GC's try and get a quad of 6n3C-E from Svetlana. They are 5881's (KT88) made in Russia in the Sovtec factory. They are a lot less expensive than 6L6GC but much better quality. I will not fit anything less in any Fender or Mesa.
5881 does not equal KT88, it is essentially an industrial quality 6L6GA/GB (aka 6L6WGB, NOT 6L6GC!) My experience with Russian made 5881 is that they will not survive where a KT88 is called for - not surprising given the difference in dissipation and voltage ratings.
- Status
- Not open for further replies.