Sad day for Marshall Lovers

Landshark · 11-09-2009, 02:13 AM

After saving up for an ungodly long time (I'm on a pretty tight budget) I finally got my TSL repaired. The tech Had 10 Hours playing time on it and said it was golden and good to go. Next day I blow another 1 w 1 ohm resistor after playing for a half hour. FML.

American Viking · 11-09-2009, 02:18 AM

Is your impedance matched? Got a blown speaker you may not have noticed yet? That'll change the impedance on you in a real sneaky way.

Take it back to the tech and make sure you clarify that he did not correct the problem.

Which specific resistor is burning up?

Landshark · 11-09-2009, 02:24 AM

Well at first it was the 1 watt 1 ohm in R9, this time it blew in R6 and you could actually see the thing blow from behing the tone shift button! It was a bright white light! I checked my cab as it is custom built to ensure it's a 16 ohm cab, which is where I've bein setting the head as well. Sure enough it is 16 ohms.

I talked to my tech yesterday and he said he wouldn't charge me for labor since it was something he initially missed. I'm hoping its not too much plate voltage being put out by the transformer, cause that would suck.

Wilder Amplification · 11-09-2009, 02:43 AM

Quote:

Originally Posted by Landshark

Well at first it was the 1 watt 1 ohm in R9, this time it blew in R6 and you could actually see the thing blow from behing the tone shift button! It was a bright white light! I checked my cab as it is custom built to ensure it's a 16 ohm cab, which is where I've bein setting the head as well. Sure enough it is 16 ohms.

I talked to my tech yesterday and he said he wouldn't charge me for labor since it was something he initially missed. I'm hoping its not too much plate voltage being put out by the transformer, cause that would suck.

Plate voltage has nothing to do with it. The valves are pulling too much current for whatever reason, either due to too hot of a bias or impedance mismatch, possibly bad OT, etc etc. 1 Amp of current will cause a 1 volt voltage drop across that 1 ohm resistor (simple Ohms law...1 Amp x 1 Ohm = 1 Volt), which would put you right at the 1 watt rating of that resistor (1 Amp x 1 Volt = 1 Watt), which means that somehow you're exceeding 1 amp of current through it, so something is definitely going on here. Could possibly be a bad OT so don't rule out that possibility.

Let us know what the tech finds.

Landshark · 11-09-2009, 03:00 AM

I'm taking it up to him Tuesday to get it looked over. I pulled the chasis out about an hour after it happened to assess the damage. It's just that one resistor. It would be my luck that it happens to be the ot. My tech said he could get them cheap though so hopefully he can pull through.

Landshark · 11-09-2009, 03:12 AM

On a side note, as soon as I get this fixed I've thought about trying some KT77s. Are any mods needed for this?

Edit: I've just had another thought. "The valves are pulling too much current for whatever reason, either due to too hot of a bias or impedance mismatch, possibly bad OT, etc etc." I bet messing with the valves is a not so great an idea given the current situation.

Wilder Amplification · 11-09-2009, 03:20 AM

Quote:

Originally Posted by Landshark

On a side note, as soon as I get this fixed I've thought about trying some KT77s. Are any mods needed for this?

Edit: I've just had another thought. "The valves are pulling too much current for whatever reason, either due to too hot of a bias or impedance mismatch, possibly bad OT, etc etc." I bet messing with the valves is a not so great an idea given the current situation.

According to the Genalex datasheet, they're pretty close to an EL34 electrically as far as bias goes. However, the KT77 is one valve I have no experience with, and going off of the datasheet, they call for a higher plate load impedance than an EL34 (4 EL34s call for a 1.7K plate-plate load whereas 4 KT88s call for a plate-plate load of somewhere between 2K-3K), so there very well may be a different OT required to run them.

Hopefully SOMEONE WITH ACTUAL HANDS ON EXPERIENCE IN PERFORMING THE EL34 TO KT77 CONVERSION can chime in here.

Landshark · 11-09-2009, 03:25 AM

I was hoping between you and AV that one of you guys could tell me something. I bet Marty would have some knowledge on the subject too.

RachelMorgan · 11-09-2009, 04:16 AM

Seriously. Get the thing working and working for a while like a few months before you try a power tube change.

Landshark · 11-09-2009, 04:23 AM

Quote:

Originally Posted by RachelMorgan

Seriously. Get the thing working and working for a while like a few months before you try a power tube change.

Which is exactly what I said in my "Edit" above. Just so we're clear that was the plan in the first place.

American Viking · 11-09-2009, 04:44 AM

I've gone the KT88 route in an amp before but not a KT77. From what I understand though it that the KT77 is a drop in replacement for an EL34 or E34L. Shouldn't need any mods other than a typical bias. Eurotubes sells complete packages specifically for those amps that have KT77's. I was going to put KT77's in my DSL but I finally managed to get rid of it.

Gtrman58 · 11-09-2009, 05:00 AM

Quote:

Originally Posted by RachelMorgan

Seriously. Get the thing working and working for a while like a few months before you try a power tube change.

This sounds like sound advice to me. Find out what wrong before you throw something new in the mix. Good Luck!

PaoloJM · 11-09-2009, 07:18 AM

A pair of KT77s ideally look for 4kohm load @ 400Vdc whereas El34s look for 3.5kohm, not enough for undue concern IMO, but worth mentioning. It would typically equate around a 1.4 ohm load difference on the secondary side.
KT77 were designed with ultralinear operation in mind.
KT77s bias slightly hotter than EL34s, due to their different transfer curves.
Other than that they're the same.
I've installed them in a number of amps (JCM800 2203 and 1959, SLP etc.) with 0 problems. They been gigged heavily in my own 2203 for 4 years now, with one swap out as part of my regular servicing.
However, I've had a couple of DSLs in with blown screen resistors and/or 22pF caps that also happened to have KT77s in there. These amps had the componants replaced and fitted with EL34s and I haven't heard any problems since. Can't say for certain that it the fault of the KT77s but I thought it worth mentioning.

Wilder Amplification · 11-09-2009, 10:24 AM

Quote:

Originally Posted by PaoloJM

A pair of KT77s ideally look for 4kohm load @ 400Vdc whereas El34s look for 3.5kohm, not enough for undue concern IMO, but worth mentioning. It would typically equate around a 1.4 ohm load difference on the secondary side.
KT77 were designed with ultralinear operation in mind.
KT77s bias slightly hotter than EL34s, due to their different transfer curves.
Other than that they're the same.
I've installed them in a number of amps (JCM800 2203 and 1959, SLP etc.) with 0 problems. They been gigged heavily in my own 2203 for 4 years now, with one swap out as part of my regular servicing.
However, I've had a couple of DSLs in with blown screen resistors and/or 22pF caps that also happened to have KT77s in there. These amps had the componants replaced and fitted with EL34s and I haven't heard any problems since. Can't say for certain that it the fault of the KT77s but I thought it worth mentioning.

This is the info we were looking for right here. Thanks Paolo.

Procter2812 · 11-09-2009, 10:53 AM

Quote:

Originally Posted by PaoloJM

A pair of KT77s ideally look for 4kohm load @ 400Vdc whereas El34s look for 3.5kohm, not enough for undue concern IMO, but worth mentioning. It would typically equate around a 1.4 ohm load difference on the secondary side.
KT77 were designed with ultralinear operation in mind.
KT77s bias slightly hotter than EL34s, due to their different transfer curves.
Other than that they're the same.
I've installed them in a number of amps (JCM800 2203 and 1959, SLP etc.) with 0 problems. They been gigged heavily in my own 2203 for 4 years now, with one swap out as part of my regular servicing.
However, I've had a couple of DSLs in with blown screen resistors and/or 22pF caps that also happened to have KT77s in there. These amps had the componants replaced and fitted with EL34s and I haven't heard any problems since. Can't say for certain that it the fault of the KT77s but I thought it worth mentioning.

Hey PaoloJM / Jon Wilder

Iv got my TSL which i found out had the 22pf cap blown. Iv ordered a new 1000v cap instead of the 500v stock one. Also a while ago i modded out the R71 resistor for a choke, but found that there was a voltage drop before the choke and it caused the PT to work harder and heat up.

Anyway now the amp has a slight buzz in the background... its the same no matter what volume. I was wandering if its the PT which is damaged or a filter cap?

Wilder Amplification · 11-09-2009, 11:04 AM

Quote:

Originally Posted by Procter2812

Hey PaoloJM / Jon Wilder

Iv got my TSL which i found out had the 22pf cap blown. Iv ordered a new 1000v cap instead of the 500v stock one. Also a while ago i modded out the R71 resistor for a choke, but found that there was a voltage drop before the choke and it caused the PT to work harder and heat up.

Anyway now the amp has a slight buzz in the background... its the same no matter what volume. I was wandering if its either the PT ( from overheating)

There will be some voltage drop before the choke due to the choke exhibiting a lower DC resistance than a sag resistor and therefore allowing the rest of the amp circuitry to draw a little more current from the power supply. However, I don't think this has anything to do with the issue that you're experiencing.

I've never seen an amp that used a 22pF cap where it does...and I find it odd that it's only on one side of the OT and jumps that side of the OT to the screen of V8. WTF is the purpose of that? If it were my amp I'd pull that out to see if there's even any difference...who knows? Could be the source of your issue. Worth checking out IMO.

How long after changing over to a choke did you notice the hum? I'd go back through and recheck your wiring...could possibly be a bad choke as well but the choke is a component that seldom fails, especially prematurely like that.

Also, what is the resistance value of the screen resistors? How many hours are on the valves?

Procter2812 · 11-09-2009, 11:13 AM

Quote:

Originally Posted by Wilder Amplification

There will be some voltage drop before the choke due to the choke exhibiting a lower DC resistance than a sag resistor and therefore allowing the rest of the amp circuitry to draw a little more current from the power supply. However, I don't think this has anything to do with the issue that you're experiencing.

I've never seen an amp that used a 22pF cap where it does...and I find it odd that it's only on one side of the OT and jumps that side of the OT to the screen of V8. WTF is the purpose of that? If it were my amp I'd pull that out to see if there's even any difference...who knows? Could be the source of your issue. Worth checking out IMO.

How long after changing over to a choke did you notice the hum? I'd go back through and recheck your wiring...could possibly be a bad choke as well but the choke is a component that seldom fails, especially prematurely like that.

Also, what is the resistance value of the screen resistors? How many hours are on the valves?

Yeah i was confused as to what its purpose was... apparently to stop parasitic oscillations?

The screen resistors seem to be 1K 5watt.

Thing is the PT was pumping out some serious heat... the front panel was hot to touch.

I used a Hammond 10 henry choke.

There is also a small hum coming through the amp when off standby? (amp not on play mode) That confuses me... should be ON standby when not playing

Wilder Amplification · 11-09-2009, 11:37 AM

Quote:

Originally Posted by Procter2812

Yeah i was confused as to what its purpose was... apparently to stop parasitic oscillations?

The screen resistors seem to be 1K 5watt.

Thing is the PT was pumping out some serious heat... the front panel was hot to touch.

I used a Hammond 10 henry choke.

There is also a small hum coming through the amp when off standby? (amp not on play mode) That confuses me... should be ON standby when not playing

Does it heat up immediately when placing the standby switch in Play mode? Or does it heat up after playing it for awhile?

Are you saying that you hear the hum when the standby switch is in Standby mode?

Procter2812 · 11-09-2009, 11:48 AM

Quote:

Originally Posted by Wilder Amplification

Does it heat up immediately when placing the standby switch in Play mode? Or does it heat up after playing it for awhile?

Are you saying that you hear the hum when the standby switch is in Standby mode?

It doesnt heat up now... it was just heating up with the choke in place. So i took it out because i didnt want to ruin my PT.

It has a little hum when the amp is in standby not playing and a buzz which is on all channels when playing. this buzz is the same tone and stays the same on each channel no matter what the volume.

Wilder Amplification · 11-09-2009, 12:02 PM

Quote:

Originally Posted by Procter2812

It doesnt heat up now... it was just heating up with the choke in place. So i took it out because i didnt want to ruin my PT.

It has a little hum when the amp is in standby not playing and a buzz which is on all channels when playing. this buzz is the same tone and stays the same on each channel no matter what the volume.

That points to a problem in the power section most likely. Wonder if you may have a filter cap that's going south.

Procter2812 · 11-09-2009, 12:13 PM

Quote:

Originally Posted by Wilder Amplification

That points to a problem in the power section most likely. Wonder if you may have a filter cap that's going south.

Yeah iv got a big blown up version of the Schematic here in front of me. Im trying to follow through to see which ones could be the culprit.

They arent too expensive... might buy some and test.

Theres two 500v caps 1nano farad and 2 350v 100uf caps then 2 315v 330uf caps These are the main suspects.

My best guess is its one of the 350v/315v caps as there are two before R71 and two after.

Maybe theres a leakage in one which is causing the hum off standby.

is there any way to test them?

Wilder Amplification · 11-09-2009, 12:21 PM

Quote:

Originally Posted by Procter2812

Yeah iv got a big blown up version of the Schematic here in front of me. Im trying to follow through to see which ones could be the culprit.

They arent too expensive... might buy some and test.

Theres two 500v caps 1nano farad and 2 350v 100uf caps then 2 315v 330uf caps These are the main suspects.

My best guess is its one of the 350v/315v caps as there are two before R71 and two after.

Maybe theres a leakage in one which is causing the hum off standby.

is there any way to test them?

Not without a capacitance meter.

Those filter caps aren't expensive...might be worth it to just buy some and swap them all out.

Procter2812 · 11-09-2009, 12:30 PM

Okay cheers for the input.. appreciate it.

Il order those four and let you know how i get on

MartyStrat54 · 11-09-2009, 02:26 PM

The EL34 and the 6CA7 share the same base (8ET) and they are very close in their characteristics. The KT77 uses a different basing. The #1 pin is NC. However, my tube manuals show that a 6CA7>EL34>KT77. The capacitance and limiting values of these tubes are very close.

The KT77 is a beam tetrode that was designed primarily for ultra-linear circuits. Unlike what you sometimes hear, that is, it is a drop in replacement for an EL34, the truth is the KT77 was designed for and is recommended for ultra-linear use.

However, similar performance can be obtained in the tetrode mode, but the output impedance will be greatly increased. For tetrode connection the fixed screen supply must not exceed 300 volts.

Also, a generous bias adjustment range should be available when using this tube in the ultra-linear mode. However, nowadays this would be almost a moot point, since ultra-linear amps have gone their course.

I personally used to think that a lot of power tubes were "drop-in's" and the bias was all you needed to worry about. This may not be the case as noted above. The main thing is that all of the online tube stores recommend a KT77 as a direct replacement for a 6CA7/EL34. This tells me that the tube is safe to use, or else they would have failures.

Personally, if I was shooting for a slightly differing tone, I would go with the Electro-Harmonix 6CA7's. They have been making this tube for quite a while and it has a very favorable performance record.

Landshark · 11-12-2009, 01:24 AM

Got an email from the guy who built my cab today... apparently he keeps records on his pc of everything he's sold and the specs on it. He said My cab was wired to four ohms and that my special comments on the order form called for an exact replica of the Marshall 1960a cab. Since the cab has two wirings, hewired it to 4 ohms. So theres my problem.

Wilder Amplification · 11-12-2009, 02:18 AM

Quote:

Originally Posted by Landshark

Got an email from the guy who built my cab today... apparently he keeps records on his pc of everything he's sold and the specs on it. He said My cab was wired to four ohms and that my special comments on the order form called for an exact replica of the Marshall 1960a cab. Since the cab has two wirings, hewired it to 4 ohms. So theres my problem.

That's lovely....build a replica of a Marshall cab, then wire it to 4 ohms.

Landshark · 11-12-2009, 03:27 AM

Quote:

Originally Posted by Wilder Amplification

That's lovely....build a replica of a Marshall cab, then wire it to 4 ohms.

I know that makes perfect sense right? Well anyway I rewired it and the heads in the shop. Hopefully I didn't destroy the transformer with my 4ohm cab... which is now 16 ohms. Perhaps the problems will cease.

solarburnDSL50 · 11-12-2009, 09:00 AM

That's disturbing. I'm glad you got it figured out but shit man, what a deal.

jcmjmp · 11-12-2009, 10:40 AM

Quote:

Originally Posted by Landshark

Got an email from the guy who built my cab today... apparently he keeps records on his pc of everything he's sold and the specs on it. He said My cab was wired to four ohms and that my special comments on the order form called for an exact replica of the Marshall 1960a cab. Since the cab has two wirings, hewired it to 4 ohms. So theres my problem.

Your cab guy is a retard. Marshall cabs are 16ohms. Some markets (like Canada) had 8 ohm cabs in the '80s... but 4 ohms? Never unless you use the stereo/mono jack that has the 4 ohm option on it.

ironlung40 · 11-12-2009, 02:08 PM

Quote:

Originally Posted by jcmjmp

Your cab guy is a retard. Marshall cabs are 16ohms. Some markets (like Canada) had 8 ohm cabs in the '80s... but 4 ohms? Never unless you use the stereo/mono jack that has the 4 ohm option on it.

no shit! the only 4 ohm setup I've ever seen is with fender combo amps, like the twin reverb. I guess the lesson from this forum is, never trust anyone. Learn how to test the most critical components of healthy tube amps yourself, like bias, impedance loads, etc. , and double check the wiring in your cabs. If you buy them new not so much, but used or custom definitely check.

11-09-2009, 02:13 AM	#1 (permalink)
Landshark Senior Member Join Date: May 2009 Location: Terre Haute, Indiana Posts: 582	Sad day for Marshall Lovers After saving up for an ungodly long time (I'm on a pretty tight budget) I finally got my TSL repaired. The tech Had 10 Hours playing time on it and said it was golden and good to go. Next day I blow another 1 w 1 ohm resistor after playing for a half hour. FML. __________________ Gibson Les Paul Studio Schecter S-1 Elite Marshall JCM 2000 TSL Vox AC 100 CPH Laney 4x12-WGS ET65's modded basketweave grill cloth

11-09-2009, 02:18 AM	#2 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 2,031	Re: Sad day for Marshall Lovers Is your impedance matched? Got a blown speaker you may not have noticed yet? That'll change the impedance on you in a real sneaky way. Take it back to the tech and make sure you clarify that he did not correct the problem. Which specific resistor is burning up? __________________ Transformers inside amplifiers were not originally designed to be in there, and the tube was not created for the guitar amp. ANY recommended idle current is a guideline and in no way a necessary requirement. There is no skeleton key for any tube amp.

11-09-2009, 02:24 AM	#3 (permalink)
Landshark Senior Member Join Date: May 2009 Location: Terre Haute, Indiana Posts: 582	Re: Sad day for Marshall Lovers Well at first it was the 1 watt 1 ohm in R9, this time it blew in R6 and you could actually see the thing blow from behing the tone shift button! It was a bright white light! I checked my cab as it is custom built to ensure it's a 16 ohm cab, which is where I've bein setting the head as well. Sure enough it is 16 ohms. I talked to my tech yesterday and he said he wouldn't charge me for labor since it was something he initially missed. I'm hoping its not too much plate voltage being put out by the transformer, cause that would suck. __________________ Gibson Les Paul Studio Schecter S-1 Elite Marshall JCM 2000 TSL Vox AC 100 CPH Laney 4x12-WGS ET65's modded basketweave grill cloth

11-09-2009, 03:00 AM	#5 (permalink)
Landshark Senior Member Join Date: May 2009 Location: Terre Haute, Indiana Posts: 582	Re: Sad day for Marshall Lovers I'm taking it up to him Tuesday to get it looked over. I pulled the chasis out about an hour after it happened to assess the damage. It's just that one resistor. It would be my luck that it happens to be the ot. My tech said he could get them cheap though so hopefully he can pull through. __________________ Gibson Les Paul Studio Schecter S-1 Elite Marshall JCM 2000 TSL Vox AC 100 CPH Laney 4x12-WGS ET65's modded basketweave grill cloth

11-09-2009, 03:12 AM	#6 (permalink)
Landshark Senior Member Join Date: May 2009 Location: Terre Haute, Indiana Posts: 582	Re: Sad day for Marshall Lovers On a side note, as soon as I get this fixed I've thought about trying some KT77s. Are any mods needed for this? Edit: I've just had another thought. "The valves are pulling too much current for whatever reason, either due to too hot of a bias or impedance mismatch, possibly bad OT, etc etc." I bet messing with the valves is a not so great an idea given the current situation. __________________ Gibson Les Paul Studio Schecter S-1 Elite Marshall JCM 2000 TSL Vox AC 100 CPH Laney 4x12-WGS ET65's modded basketweave grill cloth

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11-09-2009, 03:25 AM	#8 (permalink)
Landshark Senior Member Join Date: May 2009 Location: Terre Haute, Indiana Posts: 582	Re: Sad day for Marshall Lovers I was hoping between you and AV that one of you guys could tell me something. I bet Marty would have some knowledge on the subject too. __________________ Gibson Les Paul Studio Schecter S-1 Elite Marshall JCM 2000 TSL Vox AC 100 CPH Laney 4x12-WGS ET65's modded basketweave grill cloth

11-09-2009, 04:16 AM	#9 (permalink)
RachelMorgan Senior Member Join Date: May 2008 Location: Seattle Posts: 225	Re: Sad day for Marshall Lovers Seriously. Get the thing working and working for a while like a few months before you try a power tube change. __________________

11-09-2009, 04:44 AM	#11 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 2,031	Re: Sad day for Marshall Lovers I've gone the KT88 route in an amp before but not a KT77. From what I understand though it that the KT77 is a drop in replacement for an EL34 or E34L. Shouldn't need any mods other than a typical bias. Eurotubes sells complete packages specifically for those amps that have KT77's. I was going to put KT77's in my DSL but I finally managed to get rid of it. __________________ Transformers inside amplifiers were not originally designed to be in there, and the tube was not created for the guitar amp. ANY recommended idle current is a guideline and in no way a necessary requirement. There is no skeleton key for any tube amp.

11-09-2009, 07:18 AM	#13 (permalink)
PaoloJM Senior Member Join Date: Jun 2008 Location: Cork, Ireland Posts: 751	Re: Sad day for Marshall Lovers A pair of KT77s ideally look for 4kohm load @ 400Vdc whereas El34s look for 3.5kohm, not enough for undue concern IMO, but worth mentioning. It would typically equate around a 1.4 ohm load difference on the secondary side. KT77 were designed with ultralinear operation in mind. KT77s bias slightly hotter than EL34s, due to their different transfer curves. Other than that they're the same. I've installed them in a number of amps (JCM800 2203 and 1959, SLP etc.) with 0 problems. They been gigged heavily in my own 2203 for 4 years now, with one swap out as part of my regular servicing. However, I've had a couple of DSLs in with blown screen resistors and/or 22pF caps that also happened to have KT77s in there. These amps had the componants replaced and fitted with EL34s and I haven't heard any problems since. Can't say for certain that it the fault of the KT77s but I thought it worth mentioning. __________________ www.youtube.com/paolojm

11-09-2009, 12:30 PM	#23 (permalink)
Procter2812 Senior Member Join Date: Mar 2009 Posts: 769	Re: Sad day for Marshall Lovers Okay cheers for the input.. appreciate it. Il order those four and let you know how i get on __________________ www.sexpistolstribute.co.uk JCM800 2203X JCM2000 TSL100 Marshall 1936 Gibson Les Paul Custom Orville Les Paul Custom Fender Highway One Stratocaster Boss EQ Ibanez Tube Screamer Crybaby Wah Modded Boss TU-2 Fasel Crybaby Phase 90 MXR Boss Chorus CE-5 Boss OS-2 Modded

11-12-2009, 01:24 AM	#25 (permalink)
Landshark Senior Member Join Date: May 2009 Location: Terre Haute, Indiana Posts: 582	Re: Sad day for Marshall Lovers Got an email from the guy who built my cab today... apparently he keeps records on his pc of everything he's sold and the specs on it. He said My cab was wired to four ohms and that my special comments on the order form called for an exact replica of the Marshall 1960a cab. Since the cab has two wirings, hewired it to 4 ohms. So theres my problem. __________________ Gibson Les Paul Studio Schecter S-1 Elite Marshall JCM 2000 TSL Vox AC 100 CPH Laney 4x12-WGS ET65's modded basketweave grill cloth

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