What Variac need to test a twin reverb silverface?

[Avraxas]

Hello all!

I got a fender twin reverb Silverface from 1975 that was in a storage from more than 15 years.

I read that best way to test it (switch on) for fist time after 15 years is through Variac.

I am in EU so it will plug to 220v.

Can you please tell me how many VA at 220 volts Variac need to be at minimum?

I don’t want to risk this lovely amp and switch it with no Variac.

Thank you!

[Rontone]

It would be good to also use a 'dim bulb tester' or current limiting device when first switching on after basic tests

Have a search on the forum for topics on building one

[Avraxas]

Thank you!

Can you drive me what I need to do first please? Build a dim bulb and power on amp through Variac and dim bulb together?

Just switch on the amp with dim bulb?

What is the proper steps to start an amp that it was in storage for 15 years and that I am not sure if it’s working?

Thank you!

[Rontone]

Lots of good info and tips here on this forum,

Fender servicing:-
https://el34world.com/schematics.htm#Servicing%20fender%20amps

Power Up Amplifier First Time Procedures
https://el34world.com/Forum/index.php?topic=2376.0

Here's a few ideas at Rob Robinettes website:-

https://robrobinette.com/Tube_Amp_Startup.htm

Also building a limiter:-

https://robrobinette.com/5e3_Modifications.htm#Light_Bulb_Current_Limiter

[mresistor]

Do you think there is something wrong with it?  Or just being cautious? 


Are all the tubes installed and filaments working? speakers plugged in.  Turn the amp on in standby and check to see if all the tube filaments are lit up.


If the amp was working when it was stored it should still be working. Those amps are usually biased kind of cold so you shouldn't have too much to worry about.  Above advice is good and I'd use a limiter first.

[mresistor]

this is a good article on a LBL    https://www.bot-thoughts.com/2009/06/diy-dim-bulb-aka-poor-mans-variac.html  For a twin probably use a 100W light bulb.

[Avraxas]

Do you think there is something wrong with it?  Or just being cautious? 


Are all the tubes installed and filaments working? speakers plugged in.  Turn the amp on in standby and check to see if all the tube filaments are lit up.


If the amp was working when it was stored it should still be working. Those amps are usually biased kind of cold so you shouldn't have too much to worry about.  Above advice is good and I'd use a limiter first.

Just want to be cautious so I don’t damage anything. I don’t know the story of this amp at all. The only thing I know is that in a storage 15 years or maybe more. I don’t know even if they storage it in working order or not.


So as I understand the limiter option is the safest way to go. I will build that!

Will be in touch :)

Thank you all for the help!

Anything else I need to know please free to advise me. :)

[Willabe]

Do you think there is something wrong with it?  Or just being cautious?

He said he read the best way to turn on a long time stored amp, his amp 15 years, was with a variac.

It's because of the power supply filter caps that some say to use a variac to slowly bring up the dcv on the filter caps to reform them.

[mresistor]

Do you think there is something wrong with it?  Or just being cautious?

He said he read the best way to turn on a long time stored amp, his amp 15 years, was with a variac.

It's because of the power supply filter caps that some say to use a variac to slowly bring up the dcv on the filter caps to reform them.

Okay his question was what variac specs.. I'm quite aware of reforming caps.  Is a light bulb limiter insufficient? To answer his question look at these on ebay and find one similar to use   https://www.ebay.com/sch/i.html?_nkw=220V+variac&_sacat=0&_from=R40&_trksid=p4432023.m570.l1313


So Willabe  do you recommend using a variac along with a light bulb limiter? the op wants to know.

[mresistor]

Lets start at the beginning..   First thing I'd do with this unused twin is take the chassis out of the cabinet and then lay it down on a table of bench and then pull the doghouse  filter capacitor cover off and physically inspect the HV filter capicators.  Are there any signs of elecrolyte leakage? if so  then those that are showing signs of leakage simply have to be replaced.  In fact rather than even thinking about reforming old electrolytics, since they are very old I would just replace all of them.
And every other electroytic in the amplifier.   It's kind of the best option.

[Willabe]

Okay his question was what variac specs.. I'm quite aware of reforming caps.

Yes, but that's not what you asked.

Do you think there is something wrong with it?  Or just being cautious?

I got a fender twin reverb Silverface from 1975 that was in a storage from more than 15 years.

I read that best way to test it (switch on) for fist time after 15 years is through Variac.

Like I said, he probable read this because of people saying you need to reform the caps. So yes he's being cautious.

At 15 years sitting, I'd just use the bulb limiter by itself.

Would it be better to use both, sure, maybe, wont hurt. But your probably going to want to put in new ecaps anyway, so why bother. The bulb limiter will protect it if a ecap shorts.

[mresistor]

Not what I would do.   


I would replace every single electrolytic capacitor in the amplifier..   they are 50 years old..   reforming   variac   moot point  ..   

[mresistor]

Thank you!

Can you drive me what I need to do first please? Build a dim bulb and power on amp through Variac and dim bulb together?

Just switch on the amp with dim bulb?

What is the proper steps to start an amp that it was in storage for 15 years and that I am not sure if it’s working?

Thank you!

[mresistor]

Hello all!

I got a fender twin reverb Silverface from 1975 that was in a storage from more than 15 years.

I read that best way to test it (switch on) for fist time after 15 years is through Variac.

I am in EU so it will plug to 220v.

Can you please tell me how many VA at 220 volts Variac need to be at minimum?

I don’t want to risk this lovely amp and switch it with no Variac.

Thank you!

[mresistor]

Can you please tell me how many VA at 220 volts Variac need to be at minimum?

[Willabe]

mresistor, why did you post reply's #12/13/14?

[mresistor]

you know the answer   and you know that I probably posted those priot to your response. 


If you want to help the guy then help.  If you want to condemn my trying to help him  then carry on. 

[Willabe]

If I knew why you posted those I wouldn't be asking you.

Your way out of line here. And your not making any sense.

[Avraxas]

First I want to say a big thanks to all for your help.

Well maybe my question in title it was not the proper one.

I want to say that for sure I am gonna recap the amp. But before that, i want  first to power it up (if this step it’s safe) to see if there is a major problem with it or just need recap etc.

So what is the step i need to do first ?

Do I need Variac?

Do I need to build a current limiter?

Do I need a both in series?

Do I need first to open it up for an inspection?

After that, if the amp power up and working (or half working) I will for sure restore it.


Thank you :)

[Willabe]

So what is the step i need to do first?

Do I need first to open it up for an inspection?

Yes, always open up an amp your going to work on 1st.

Do I need to build a current limiter?

Yes, I would just use a current limiter by it self for 1st start up. If a power supply filter cap shorts out, the limiter should/will protect the amp. Just keep you finger by the amps power switch just in case. If the bulb lights up bright and stays bright, or you see/smell smoke, see sparks, turn the amp off.

After you make the limiter, test it with a known working tube amp to see how the bulb lights up and how long it takes, a few seconds, to go back down dim.

Do I need Variac?

I would say no, not for this.

Guys use a variac to start up old amp that have been sitting for a long time to reform the filter caps slowly. They bring up the acv slowly, over a day or more. But this is usually for old stereo amps that you cant get the caps for anymore. They used some pretty big caps in a lot of those old stereo's. If they can save the caps, then they don't have to try to make something fit in the space in the chassis where the old caps are.

You don't have this problem.

Do I need a both in series?

You could, it won't hurt, but I wouldn't feel the need to use both on that amp. And if I did use a variac with the limiter, I wouldn't use it to reform the caps over many hours. I'd just slowly bring up the acv wall voltage over a minute or so.

The light bulb limiter does slow down the in rush dcv to the caps to help protect them from giving up the ghost. The variac will slow it down some more.

Pull the chassis, open the dog house, cap cover on the back of the amp, and look for caps leaking goo. A little, they probably won't blow. If their really bad, then they might. But I still think the limiter will save the amp. If you have the right size bulb in it. For a Fender Twin with 4x6L6's, you want a 100w bulb, not larger.

[Avraxas]

Thank you very much! :)

Ok. I do this steps!

About 100W bulb. i am not in US and we have 220v, still ok yes?

And one more question (maybe silly but), it is better the first switch on with the current limiter bulb circuit that I will build to make it with NO tubes is socket?

Oh and one more thing. Just in case I want to buy a Variac for later purposes. 500VA one it’s ok or better buy a 1000VA one?

That’s it! I finished with questions! :D

[Avraxas]

Some photos:

[Avraxas]

I don’t see anything suspicious inside. Also the big filter capacitors have no leak.

I move on current limiter bulb circuit, and when I build it I will power on this baby!

Crossing fingers! :)

[Willabe]

About 100W bulb. i am not in US and we have 220v, still ok yes?

Yes.

It's the bulbs filament that's important here, not the voltage. The more current that gets pulled through the bulbs filament, the brighter it glows. That's what limits the current draw, the filament. The smaller the filaments wattage, the more protection/limiting it gives. With a 2X6L6 and a 6V6 amp, I use a 60w bulb. This gives a little more protection.   
 

And one more question (maybe silly but), it is better the first switch on with the current limiter bulb circuit that I will build to make it with NO tubes is socket?

Yes, with all the tubes in. The tubes will draw current. That makes the amps power supply have the normal working strain on it.

Turn the amp on, let the tubes warm up for a minute or so, then flip the standby switch. The bulb should glow brightly then dim back down. If this happens then you can turn off the amp and disconnect it from the bulb limiter.

Then after you do any work on the amp, like after changing all the power supply filter ecaps, you test the work you did with the bulb limiter. You do this so you don't burn up the amp from something you mis-wired.

Same thing, with the bulb limiter hooked up to the amp, turn on the power switch, with the standby switch off, let the tubes warm up a little, put the standby switch in play, watch the bulb, should glow brightly for a few seconds, then dim back down. If this happens, you can remove the bulb limiter and then check for the correct dcv's in the power supply and the tubes.

[Willabe]

Lots of good info and tips here on this forum,

Fender servicing:-
https://el34world.com/schematics.htm#Servicing%20fender%20amps

Power Up Amplifier First Time Procedures
https://el34world.com/Forum/index.php?topic=2376.0

Here's a few ideas at Rob Robinettes website:-

https://robrobinette.com/Tube_Amp_Startup.htm

Also building a limiter:-

https://robrobinette.com/5e3_Modifications.htm#Light_Bulb_Current_Limiter

This above is all things you need to read up on and understand.

Make sure you understand how to bias up the power tubes in that amp. They are push/pull (PP) class AB grid bias.

[Willabe]

And this, Merlin's web site;
 
https://www.valvewizard.co.uk/

[Rontone]

On the pictures you posted, the caps have some swollen/bulging areas, this is another warning sign to look out for as well as actual oil leaking from the body

The power tube sockets have one screen resistor replaced, its hanging way too loose and may touch something like the mounting bolt next to it, best to replace all with something fresh, but something has happened there before, looked like the whole area got really hot at some point,

Also at the very far end power tube it looks like the screen resistor has really cracked through and will need replacing

I can see the heater wiring near the replaced screen resistor looks scorched a bit, check the wires insulation for breaks/splits or replace, you do not want a heater winding short....

Some resistors look a little crispy, have a slow look through the amp and look for anything suspicious, or charring/blackening and cracking on any components,

[Avraxas]

Thank you very much both! You really help me very much! I will double check everything more carefully and I will be back with news! :)

[Avraxas]

Also at the very far end power tube it looks like the screen resistor has really cracked through and will need replacing

True!

[Avraxas]

Just wonder why is the video to build a current limiter bulb circuit (Build Your Own Current Limiter for Protection when Repairing and Testing Electronic Equipment) the guy say that "the more Watts the bulb is, the better" I am asking not for now but in later use in other amps that maybe got in the future.

Is there any "math type" to know what watt bulb I can use in other situations?

Can someone explain me please?

[Rontone]

Here is a good explanation using some different wattage of bulbs, about 1/2 way down the page in the 'Using the tester' section

https://antiqueradio.org/dimbulb.htm

As Willabe said, a 100w bulb will be fine for a 4x6L6 Twin amp, to 'see the way the glow changes', too high wattage bulb and you won't see the glow, and then too low like a 40w bulb you won't see it go dim

Must be old type incandescent bulb only, no LED, no fluorescent or any new modern type bulb with a circuit inside

[Willabe]

As Willabe said, a 100w bulb will be fine for a 4x6L6 Twin amp, to 'see the way the glow changes', too high wattage bulb and you won't see the glow, and then too low like a 40w bulb you won't see it go dim

It's more about the protection it gives.

The smaller the bulbs filament, lower wattage, the less current can be pulled through it. And we're using it to protect against a direct short in worse case scenario.   

[Avraxas]

As I need to replace the the 4x screen resistors in power tubes, I am thinking to choose Vishay "PR01, PR02, PR03 Power Metal Film Leaded Resistors"

Original the twin reverb have 1W resistors but I read that better go for 2W or 3W?

Your opinion about Vishay Resistors and what Watt I should put?

https://www.vishay.com/docs/28729/pr010203.pdf

I will also order filter Capacitors F+T brand

[Willabe]

You should start a new thread in Tube Amp Building - Tweaks - Repairs.

[Avraxas]

You should start a new thread in Tube Amp Building - Tweaks - Repairs.

Yes I will. It’s better that way! Thank you