# New tubes in Marshall, instant blown ht fuse?



## Destracted (Aug 20, 2021)

I have a tsl 100 made in late 2003 that ive owned around 5 years. They obviously have a reputation for runaway bias blowing tubes but its always worked perfectly, and i believe its the newest revision board. I bought a new set of matched tubes to replace what was in there, they are old and it will pop a bit when cold. I checked the bias before pulling them and both sides were a steady .081. I swapped out all the tubes and fired on the amp ready to check the bias again. I got no reading at first but after checking and rechecking and flicking the standy a couples times the amp started getting noisy and the 2nd PA tubes lit up like a bulb and made an audible pop. As a result the HT fuse blew. When I turn it on the 4 PA tubes do glow lightly, all the same from what I can tell but Ive had to order more fuses.
Im not sure what caused it. If somehow I crossed the positive bias posts or if somehow the new tubes caused it. Anyone have any thoughts or suggestions?


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## nonreverb (Sep 19, 2006)

Destracted said:


> I have a tsl 100 made in late 2003 that ive owned around 5 years. They obviously have a reputation for runaway bias blowing tubes but its always worked perfectly, and i believe its the newest revision board. I bought a new set of matched tubes to replace what was in there, they are old and it will pop a bit when cold. I checked the bias before pulling them and both sides were a steady .081. I swapped out all the tubes and fired on the amp ready to check the bias again. I got no reading at first but after checking and rechecking and flicking the standy a couples times the amp started getting noisy and the 2nd PA tubes lit up like a bulb and made an audible pop. As a result the HT fuse blew. When I turn it on the 4 PA tubes do glow lightly, all the same from what I can tell but Ive had to order more fuses.
> Im not sure what caused it. If somehow I crossed the positive bias posts or if somehow the new tubes caused it. Anyone have any thoughts or suggestions?


Did all 4 start glowing bright?


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## Destracted (Aug 20, 2021)

nonreverb said:


> Did all 4 start glowing bright?


No, just the 2nd one. it happened really fast.


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## nonreverb (Sep 19, 2006)

I suspect it's defective out of the box. It happens occasionally.


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## Destracted (Aug 20, 2021)

nonreverb said:


> I suspect it's defective out of the box. It happens occasionally.


Ya, I was wondering about that. Ill try swapping them back and seeing what happens when the fuses arrive.


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## Latole (Aug 11, 2020)

Use a current limiter bulb lamp, you'll save fuse and make tubes ( and amp) tests easier.


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## Latole (Aug 11, 2020)

Destracted said:


> I checked the bias before pulling them and both sides were a steady .081.
> 
> Anyone have any thoughts or suggestions?


0.81 ma at what plate voltage ? 

JJ EL34 specs ; 25 watts / tube
Bias should be not over 70% plate dissipation= 18 watts.
I like more 60% 
17.5 watts = Plate voltage X cathod curent ( 0.080 ma / 2 ) 
Or for two tubes; 
35 watts = Plate voltage X 0.080 ma ( your reading) 
35 / 0.08 = 437

Plate voltage must not be over 437 volts

Without knowing the plate voltage, the bias will only be approximate with its consequences


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## Destracted (Aug 20, 2021)

it might have been .0081 now that I think about it. its never been an issue, it doesnt even run hot.


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## Latole (Aug 11, 2020)

It is so easy to read plate voltage *if *you know what you do.


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## nonreverb (Sep 19, 2006)

Latole said:


> It is so easy to read plate voltage *if *you know what you do.


Latole, I agree that the plate voltage was a wee bit high with the original tubes installed however they were there a long time and no failures. When he replaced them, one was glowing bright right away which suggests a defective tube. He's on the right track by swapping back to confirm that there might be a tube fault....why confuse the situation with information he does not need at this time?


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## Latole (Aug 11, 2020)

If our friend Destracted installs exactly the same brand of tubes (which we don't know) the bias could be left out.
Even if I never do that.
If on the other hand it is not the same brand, nothing says that the performance nor the longevity of the tubes will be the same.

If Destracted don't have knowledge about bias adjustment, It is another story


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## nonreverb (Sep 19, 2006)

Latole said:


> If our friend Destracted installs exactly the same brand of tubes (which we don't know) the bias could be left out.
> Even if I never do that.
> If on the other hand it is not the same brand, nothing says that the performance nor the longevity of the tubes will be the same.
> 
> If Destracted don't have knowledge about bias adjustment, It is another story


Granted, the OP has not indicated that the replacement set are matched. That said, an immediate red plating tube suggests a defect. Power tubes can take an under bias with no signal. It's not recommended but the current through those tubes is far higher when they are operating with signal applied. Therefore, one can assume that one, the offending tube is defective or there's a bias supply problem in the amp.....The OP is doing the right thing by swapping back the power tubes to observe the operation before the replacements were installed and can assess from there if the new set has a defective tube.


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## Destracted (Aug 20, 2021)

Yes, the replacements are fully matched and brand new JJs. It was the second tube that lit up. It happened inside of 5 seconds of flipping the standby switch, if it was a bias drift like these amps are notorious for it would likely take much longer as well as require some actual signal to push it (I assume). Ive previously left this amp on for over a full day just to test it for overheating which its never done even though these are known for running hot.


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## Destracted (Aug 20, 2021)

Latole said:


> If our friend Destracted installs exactly the same brand of tubes (which we don't know) the bias could be left out.
> Even if I never do that.
> If on the other hand it is not the same brand, nothing says that the performance nor the longevity of the tubes will be the same.
> 
> If Destracted don't have knowledge about bias adjustment, It is another story


I did enough research on how to set it up to know the proper procedure. I used a multimeter set to DC Volts. I never touched either of the bias pots, I only tested the posts and given the videos Ive seen of others with the same amp I was pleasantly surprised they were both the same as well as rock steady. This does not seem to be the usual case with TSLs. However Im obviously too inexperienced to remember whether I read .0081 or .081. I realise guys prefer them a bit cooler (.0075) but this thing sounds awesome, especially clean so Im probably going to leave it around the same with new tubes.


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## Latole (Aug 11, 2020)

If original tubes are Sovtek ans IF the bias was the good one, JJ's tubes may need a new bias.

Adjust bias more cooler you can if you like the sound of the amp.

Cooler bias is alway more safe.


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## Destracted (Aug 20, 2021)

Latole said:


> If original tubes are Sovtek ans IF the bias was the good one, JJ's tubes may need a new bias.
> 
> Adjust bias more cooler you can if you like the sound of the amp.
> 
> Cooler bias is alway more safe.


I posted a picture of them, there is no brand name they just identify as Russian with a logo Im unfamiliar with.

1 thing I now realise I didnt notice last night is 1 of them (the same slot as the 1 that red plated...) has a different number on it despite looking otherwise idenical. It says 0314 but the rest are 0251


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## Latole (Aug 11, 2020)

Russia made tubes are often Sovtek, never JJ's


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## nonreverb (Sep 19, 2006)

Destracted said:


> I posted a picture of them, there is no brand name they just identify as Russian with a logo Im unfamiliar with.
> 
> 1 thing I now realise I didnt notice last night is 1 of them (the same slot as the 1 that red plated...) has a different number on it despite looking otherwise idenical. It says 0314 but the rest are 0251
> View attachment 383564
> ...


Original Svetlana tubes (aka Winged C) before Mike Matthews got a hold of the brand name. Those are well regarded tubes. The numbers are the date codes.


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## Latole (Aug 11, 2020)

You are right original tubes are Svetlana


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## Destracted (Aug 20, 2021)

Latole said:


> Russia made tubes are often Sovtek, never JJ's


Obviously. I never thought they were. The new tubes are JJs, as pictured previously shown installed in the amp above. You are confusing the old tubes with the replacements but I think ive been pretty clear.


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## Destracted (Aug 20, 2021)

nonreverb said:


> Original Svetlana tubes (aka Winged C)before Mike Matthews got a hold of the brand name. Those are well regarded tubes. The numbers are the date codes.


Great, if they are just date codes then that seems fine. It sounds like a bad tube. Ive contacted the seller on Ebay and will look to return them. They were a sealed, matched quad as advertised but my guess is one took damage during shipping or sometime after they were matched and packaged at Apex.

I appreciate all the help with troubleshooting guys, thanks a bunch.


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## Paul Running (Apr 12, 2020)

Destracted said:


> I checked the bias before pulling them and both sides were a steady .081.


You were probably measuring .081VDC, 40mA each tube. The schematic indicates that both tubes on each side, share one resistor....081VDC across 1Ω equates to 81mA, plate + screen current, for 2 tubes. A more accurate method is to use a bias meter which measures strictly the plate current for each individual tube. When purchasing output tubes for your amp, because it uses a quad, you may wish to buy them in sets of 8, octal matched-set. The excerpt from the schematic below, indicates the cathode circuitry, high-lighted in yellow....what you are measuring at the test points with your DVM.









I've attached the complete schematic.


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## Paul Running (Apr 12, 2020)

An adapter for measuring plate current of common octal amp tubes:


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## Destracted (Aug 20, 2021)

The seller has told me he will send me a replacement tube. I sent him tbe info on the label so hopefully it will match.


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## player99 (Sep 5, 2019)

Did I miss you put the old tubes back and it worked?


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## Destracted (Aug 20, 2021)

player99 said:


> Did I miss you put the old tubes back and it worked?


No, I put them back in but I wont have a replacement HT fuse until tuesday when it shows up from amazon. Further I would hope the blown fuse would have prevented any greater damage and that my amp still works. It still lights up and all switches still function. It seems a given that its a bad tube at this point, I dont think a likely alternate conclusion has been put forward but who knows I guess.
The seller has now asked me to send the EL34s back to him and he will replace all 4 with a matched quad. I will update the thread as it plays out. Thanks again to everyone for their time and interest.


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## nonreverb (Sep 19, 2006)

Destracted said:


> No, I put them back in but I wont have a replacement HT fuse until tuesday when it shows up from amazon. Further I would hope the blown fuse would have prevented any greater damage and that my amp still works. It still lights up and all switches still function. It seems a given that its a bad tube at this point, I dont think a likely alternate conclusion has been put forward but who knows I guess.
> The seller has now asked me to send the EL34s back to him and he will replace all 4 with a matched quad. I will update the thread as it plays out. Thanks again to everyone for their time and interest.


That's what the fuse is for. Without it the light show and potential camp fire would be impressive.


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## greco (Jul 15, 2007)

nonreverb said:


> ...the light show and potential camp fire would be impressive.


Excellent description! 
Your "literary" side of electronics theory is showing.


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## jb welder (Sep 14, 2010)

The TSL has bias test points. 90mV (.09V) is the factory recommended setting (it is per pair of tubes in the 100W models). Going a bit cooler with .08V is good practice (like Latole suggested). 
He is doing it right.


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## Paul Running (Apr 12, 2020)

Here's a chart to record voltage measurements for your output tubes. If you take the readings when the amp is in tip-top shape, they will serve as a reference when performance takes a nose-dive...prepares an early troubleshooting plan of attack.


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## Destracted (Aug 20, 2021)

You guys are great. Thanks for all the tips. These TSLs dont get a lot of love but I think its fantastic, though it did take me a long time to really understand how to dial it in correctly. After I bought my rectoverb combo last year and started A/B testing them back and forth it really excellerated the process. I bought the Mesa up and right away was convinced the Marshall sounded thin compared to it , but then Id work with it until it sounded better than the Mesa. I must have went back and forth a dozen times until they both sounded amazing. I thought the Marshall was old news after the little dual rec showed up but now I realise how great the TSL actually is. The next big turning point was using an OD with the gain turned all but off and the volume cranked. It brought this amp to life.


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## Paul Running (Apr 12, 2020)

If or when the under-side of the chassis is exposed, you may wish to ensure that all the connectors are secure. Those connectors may not have locking connectors...I've seen them come loose and there are quite a few of them.


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## Destracted (Aug 20, 2021)

UPDATE:

Fresh fuses arrived today so I installed 1 and fired up the JCM with the original power amp tubes. It works great and the new preamp tubes make for a quieter noise floor. Awesome.
I decided not to mail the JJs off just yet because I wanted to test them 1 more time this time without even touching the bias posts. immediatly I noticed the amp was much noisier, to the point it sounded like it was busting at the seams, and POP, it once again blew the HT fuse inside of 10 seconds of switching the standby. So Ive packed up the 4 JJs and am sending them back for replacements. Ill update when the fresh set arrives.


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## Paul Running (Apr 12, 2020)

I noticed on their website that they keep detailed test records of your tubes...it may be worth requesting a copy of such.

"We keep extensive records of the characteristics of your tube (more than will fit on the label!)"


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## Hammerhands (Dec 19, 2016)

Someone posted a video a few weeks back where the tube sockets on an old Marshall were beat.

The pins were not grabbing, the connections were dirty, it was causing intermittent connections and blowng fuses.

I wonder if the pins on the tubes were a little thinner or off, if it would cause similar issues.


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## Destracted (Aug 20, 2021)

Hammerhands said:


> Someone posted a video a few weeks back where the tube sockets on an old Marshall were beat.
> 
> The pins were not grabbing, the connections were dirty, it was causing intermittent connections and blowng fuses.
> 
> I wonder if the pins on the tubes were a little thinner or off, if it would cause similar issues.


Im sure the guitar shop will test them and let me know what they think before shipping out any new tubes.


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## Destracted (Aug 20, 2021)

The new tubes arrived and they work, no blown fuse! The noise floor is way down now. The popping and hissing is all gone. The only problem is a weird sort of unpleasent phaser type sound on the low strings .(EDIT: fixed, not the amp) Im guessing this is because I havent touched the bias pots yet. Im a bit scared tbh. That is next.


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## Destracted (Aug 20, 2021)

Biased up to .086 on both sides, perfectly stable. The little amount you turn the pots for huge swings is pretty crazy. you just tap the screw driver on it and it swings .01. Amp is like new now. Thanks to everyone for your help and time.


* The phasing issue wasnt the amp. It was actually this 2004 Deluxe strat I recently bought. Restrung it yesterday with lighter strings which dropped the bridge back, which lowered the string height a bit and it was fretting out ever so slightly causing a weird warble. doh!


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## Patrice Brousseau (Aug 12, 2020)

Paul Running said:


> An adapter for measuring plate current of common octal amp tubes:
> View attachment 383578


Homemade Paul?


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## Paul Running (Apr 12, 2020)

Patrice Brousseau said:


> Homemade Paul?


The one I have is a DIY, 2 adapters, 1 meter and a switch to select the tube...for dual tubes:


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