Scott F: Please read. Another JTM question

[benjaturner]

Or if anybody else knows the answer I'd love to hear it. I was talking to a member yesterday names Jeff Seal about my Marshall JTM60. He was very helpful and gracious in describing a very simple mod I could perform on my amp. This basically involved removing the rectifier, and it's corresponding capacitors, from the pre-amp valves so they would run on a DC current. I was all set to do this today after Jeff Seal listed a very detailed account of the steps I should take in performing the mod when my dad said I should try and get a second opinion before. I don't mean to undermine Jeff Seal's obviously substantial knowledge of amps but I thought it would be irresponsible of me to go ahead with the mod without investigating further.

The ongoing problem that brought about my queries was the components directly next to the valves burnt out or unsoldered themselves from the generated heat. It turns that these component aren't neccessary to the performance of the amp, so I wouldn't lose anything by taking them out.

The reason I ask for Scott F's opinion is that I remember you telling me a while ago that you have/had the same amp. Have you ever heard of anything to do with this matter? Or has anyone else for that matter?

Thanks for reading,
Benja

 

[Artie]

Re: Scott F: Please read. Another JTM question

I'm not expert in guitar amps at all, but if you remove the rectifier and caps, it will be running on AC - not DC. The rectifier is what makes it DC. And the AC will be at 60hz. I don't know who Jeff Seal is, but this sounds like a horrible idea. There's a reason amps are built with power supplies.

Edit: Actually, if you remove the rectifier, it won't run at all unless you reinstall jumpers in the right place.

 

[Scott_F]

Re: Scott F: Please read. Another JTM question

When it comes to amp mods and general amp knowledge, I bow in Jeff Seal's direction. If he says it, I say word.

 

[STRATDELUXER97]

Re: Scott F: Please read. Another JTM question

Jeff Seal is a very well known and respected amp guru guy for certain! ;o)

Artie...I was surprised to see you didn't know Jeff?

 

[Artie]

Re: Scott F: Please read. Another JTM question

Jeff Seal is a very well known and respected amp guru guy for certain! ;o)

Artie...I was surprised to see you didn't know Jeff?

Actually, the name rings a bell, I'm just not sure from where. I suspect that benja misunderstood the directions. I can't imagine an amp "mod" that removes half the power supply.
Tubes need DC - and lots of it. :laugh2:

Edit: The more I think about this, the more I think I realize whats going on. I imagine Jeff was refering to removing the solid state rectifier, and replacing it with a tube rectifier. Now that makes sense.

 

[Scott_F]

Re: Scott F: Please read. Another JTM question

No, he's refering to the 6.3volt tube heater current. It's AC in most amps. DC is not the preferred way. People talk about AC being more noisy, but I do not find it to be a problem at all. Jeff's take was that the DC is just tough tough on the solder joints in that particular amp. (probably not that well put together I'm assuming)

If I read it correctly last night, ALL he is saying is to convert the tube heaters back to AC instead of DC. Which will still heat the tubes just fine.

Your power transformer takes in 110 or 220volt and then converts it, steps it up or down depending on the application. It runs that higher voltage in AC over to the rectifier where it is converted to DC. The 5volt AC taps heat up the rectifier and the 6.3volt AC taps heat up all the other tubes.

One other thing, I prefer to not use the 6.3 AC tap to power up the pilot light on my Franklin. I am using 110v pilot lights that work great and don't pull any load at all from the 6.3volt taps. Just a matter of personal preference.

 

[benjaturner]

Re: Scott F: Please read. Another JTM question

sorry everyone for the confusion. Yeah. If you remove what I think Jeff called the rectifier then the valves run in AC current. Is that right?

Scott F, You nailed it about Jeff Seal. In the describtion he sent me he knew the names of the capacitors I had to take out!!! I'm quite obviously an absolute amateur regarding this stuff but that totally blew me away. Maybe I'm over-reacting but that seems amazing to me.

Incase Jeff reads this thread I hope you aren't offensed in any way by my seeking conformation on your reccomendations. I would like to once again extend my gratitude for your help.

Many thanks,
Benja.

 

[the guy who invented fire]

Re: Scott F: Please read. Another JTM question

I want it to be known , that Jeff Seal is the man with Tube amps!

If he gives you advise, you take!

 

[Scott_F]

Re: Scott F: Please read. Another JTM question

sorry everyone for the confusion. Yeah. If you remove what I think Jeff called the rectifier then the valves run in AC current. Is that right?

Scott F, You nailed it about Jeff Seal. In the describtion he sent me he knew the names of the capacitors I had to take out!!! I'm quite obviously an absolute amateur regarding this stuff but that totally blew me away. Maybe I'm over-reacting but that seems amazing to me.

Incase Jeff reads this thread I hope you aren't offensed in any way by my seeking conformation on your reccomendations. I would like to once again extend my gratitude for your help.

Many thanks,
Benja.

He's not telling you to remove the rectifier. No way. Amp won't run with out some sort of rectifier.

I don't want to insult you, but it doesn't seem that you know what you are doing at all. I could care a less if you kill your amp, that's your business. I just don't want to see you get killed yourself. There are LETHAL voltages inside that amp. Do you know what not to touch? Do you know how to drain capacitors? If not, that's where you need to start learning. Lots of great info on the net about this stuff.

Again, no insult meant. Just know what you are doing because its freaking dangerous if not.

 

[benjaturner]

Re: Scott F: Please read. Another JTM question

My GCSE electronics teacher told me that if I leave a circuit unplugged for half an hour then that would drain the capacitors. Is that right? That's what I've always done, just unplug the amp and leave it to stand for at least half an hour then get on with whatever I'm doing.

I'm pretty sure Jeff refered to the 'black box' as a rectifier. Component designation DB1.

Thanks,
Benja

 

[Pepi]

Re: Scott F: Please read. Another JTM question

My GCSE electronics teacher told me that if I leave a circuit unplugged for half an hour then that would drain the capacitors. Is that right? That's what I've always done, just unplug the amp and leave it to stand for at least half an hour then get on with whatever I'm doing.

I'm pretty sure Jeff refered to the 'black box' as a rectifier. Component designation DB1.

Thanks,
Benja

NO! you discharge the caps before doing anything .... OR :dance: Not all circuits are designed to discharge when power is not applied.

 

[benjaturner]

Re: Scott F: Please read. Another JTM question

Could someone please explain how I can discharge the capacitors please. Also, I forgot to ask earlier, for the jumper leads I'm guessing I need some sort of shielding to ensure the jumper leads don't touch and short circuit. Can I just use any shielded wire I can find around the house or is there a specail type I need to buy?

Thanks,
Benja

 

[Scott_F]

Re: Scott F: Please read. Another JTM question

http://www.firebottle.com/fireforum/fireBB.cgi?cfg=dlx&enter=go

Lots of good reference info on the right side of this website.

 

[Jeff Seal]

Re: Scott F: Please read. Another JTM question

...well, where to start.... first thanks for the kudos....

benja, I openly welcome seeking out info that helps us understand things. I will not ever claim my words to be "gospel", but rather very well thought out and "tried and true" experiences... I am an amp tech, and am fortunate to get to "play" with everyone else's toys on a daily basis....(I get paid to play through Bogner's, Diezel's, CAE's, old Fender's, Marshall's, Hiwatts and quite a few amps that very few have even heard of!........rough gig.. huh?.. )

Shop website is:

www.speakersurgeon.com

and my phone is (281) 922-5662...feel free to call me...

I do wish everyone was as "thorough" about the info they recieve online as you are...... I realize we have never met, and neither of us "know each other from Adam", but I do promise eveything I post to be "accurate" or else I will not post it!

There are some really great people here with a wealth of knowledge.... which is what makes this site so incredibly cool...

The rectifier for the Heater voltage should not be confused with the HV (High Voltage) rectifier....just to clarify...

Pepi is absolutely correct, unless you "make sure" the filter caps are discharged...they aren't! Lots of info out there, I use a 220 ohm 10 watt resistor (this gives you lots of non conductive area to hold on to) and short the caps with this.......Do "dead short" the caps AFTER this, just to be on the safe side..)

take care....

Jeff Seal

..just as an "afterthought"..... I might suggest you leave this to somebody more experienced if you have ANY doubts about this at all!..... for real!

 

[tone?]

Re: Scott F: Please read. Another JTM question

Dude i have one of these amps and i am pretty sure the caps discharge themselves when you turn the amp off. that is the clicking noise i think that you get when you power off.
but i would TOTALLY LISTEN TO THE OTHER GUYS AND TRY TO DISCHARGE THEM.

i really dont like this amp anymore. it has given me so many problems and im selling the sucker for 600euro.
it sounded pretty darn good when i first got it and broke it in a bit but now it sounds pretty pooy.

im gonna get a boutique instead.

what will this do to the sound of this amp that Jeff told you to do?

i tryed to do some mod on this amp and everyone just turned away when they saw the inside. including some people on the net.

 

[JeffB]

Re: Scott F: Please read. Another JTM question

Don know a damn thing about modding amps or all the techno mumbo jumbo..but I know a thing or two about the JTM60.

My suggestion..sell it ASAP. Or spend the $ and let someone like Jeff or Trace at Voodoo totally re-build the dang thing.

 

[rinse_master]

Re: Scott F: Please read. Another JTM question

Dude i have one of these amps and i am pretty sure the caps discharge themselves when you turn the amp off. that is the clicking noise i think that you get when you power off.

My atomic reactor does that, I thought it was just the tubes cooling down again?, it oly has an input and a power switch, so not a whole lot of discharging to do...

 

[PUCKBOY99]

Re: Scott F: Please read. Another JTM question

Benja....are you in the U.S. ???

I would suggest you have a professional do the job....& if there's no one in town that you trust, send it to Jeff.

If you haven't heard of Jeff, he's in the same ballpark as Scott Splawn & Trace at VooDoo Amps. He knows what he is doing, has a great reputation, & in my experience, having been around here for a while, he is a top notch class act & he will do the job right...THE 1ST TIME!

 

[Rich_S]

Re: Scott F: Please read. Another JTM question

I had a business meeting right up the street from Jeff Seal's shop this morning, so I stopped by to meet him afterwards. (Nothing like standin' around shootin' the sh*t about guitars and amps on company time!)

Jeff's the real deal. He showed me a Marshall JCM800 head (one of those nasty channel-switching ones) that he has gutted and rebuilt as point-to-point with a Fender clean channel and a Marshall-and-then-some dirty channel. Nice workmanship throughout.

So, his advice on your amp is good. However, if you don't know the difference between the filament (heater) supply and the main B+ supply, either 1) take it so someone else, or 2) read and learn before you go messin' around in a tube amp. AX84.com and 18Watt.com are the places where I learned. And the first thing you need to learn is how to drain and check the filter caps before you start. At the very least, 400 VDC hurts.

 

[Artie]

Re: Scott F: Please read. Another JTM question

The rectifier for the Heater voltage should not be confused with the HV (High Voltage) rectifier....just to clarify...

Hey Jeff; Thanks for popping in, and thanks for clarifying that. I was racking my brain trying to figure out why someone would remove the main bridge rectifier. :laugh2:

The few tube amp schematics I've seen didn't have heater rectifiers, so that never occured to me. (Until Scott mentioned it, of course.)

Artie