[Jblue76]

Hey All,
I could really use your help! I’ve got a ‘68 drip edge twin with a nice pair of k120s and I want to get it running quieter and fully optimized for a sweet JG tone. I’d like to go to the amp tech with a clear list of work to be done, but I know basically nothing about electronics and am pretty confused by all that my google searching has turned up. So, I thought I’d defer to you experts that make up this awesome community and get some clarity in the matter.

The amp has already been blackfaced (though there is Reverb on the normal channel, less than on the vibrato channel, but it’s there), caps were replaced a couple years ago, and the tubes are all original (tested fine when it was serviced).

I am hoping you all will be able to let me know if I’m on the right track or not. The following is what I gather I am supposed to tell the tech I want (though I really don’t understand it all):
— .022uFs in the tone stack.
— non-inductive metal film plate resistors.
—change all of the cathode resistors with military grade axial lead tantalum capacitors and do this for the bypass caps as well.
— do I ask him to disconnect the vibrato?
—do I want him to jumper channels in some way?
— do I get him to do something with the input that reduces noise?
—are there any other aspects of the Healy mods I should get done?

Thanks in advance everyone!

[Pointclear]

I spent the last year working on my 73 master volume twin and I now have it almost exactly perfect. Every amp is a little different and your tone will ultimately be a sum of the whole rig. I would really advise you to study up and get confident to do at least some of the finer tuning stuff on your own. Unless your tech is very schooled in subtle Jerry tone, you may be more satisfied and better off financially doing the tone chasing yourself. I spent countless hours changing out caps and resistors all over the amp,one at a time, then plugging in and listening.

You are ahead of the curve with the old tubes. They will make a huge difference. Check to see if you have the tone killing caps on your power tubes and remove them.

As far as the changes I made: I did what you are describing with the tone stack, tantalum bypass caps, and dale metal plate resistors. Each material makes a huge difference in tone and feel to me. Orange drops are not all equal, and the 225p series are really where it’s at 90% of the time. I disconnected the vibrato as well.

I also did a lot of tweaking in the phase inverter and phase inverter input using different values and component materials. I settled on xicon metalized film caps in the phase inverter because they were more 3-d and tighter in the bass. A lot of my work was done to tighten the bass response, and my next step will be to put in larger filter capacitors.

I also replaced the 820 ohm reverb return resistor with a 2200 ohm resistor - big push in gain and texture. Your reverb circuit may be different than mine, though. Oh, I also left the f&t electrolytics in place on the reverb circuit instead of using the tantalum caps. I felt I got a more expansive and juicy sound with the electrolytics. The tantalum caps have a thinner faster sound.

I also put reverb on both channels and put both channels in phase with one another, so that I can jumper them if need be ( which I do not normally do).

Good luck with everything! And let’s us know how it goes!

[Jblue76]

Thank you so much for that detailed reply. It defiantly helps give me confidence that I’m on the right track. You know, I’ve thought for a while about demystifying the technical work and just learning how to do it myself like you’re suggesting, but I never follow through for fear that I’ll screw things up or electrocute myself... man, I’ve never even soldiered before... anyhow, hopefully I’ll manage to sneak away from the kids long enough to get my twin to the tech sooner than later. Are these materials the kind of thing a tech would have around or are most of them pretty specialized and would need to be ordered? I’d like to work it so the amp is away from active service for as short a time as possible!
Thanks again!!!

[waldo041]

— .022uFs in the tone stack.
or .02uF MYLAR/POLYESTER

— non-inductive metal film plate resistors.
MIL SPEC RN Type use the 70's for the plates more robust.

—change all of the cathode resistors with military grade axial lead tantalum capacitors and do this for the bypass caps as well.
no ONLY the cathode bypass capacitors use Mil Spec CSR13 type

— do I ask him to disconnect the vibrato?
Have them install what is now called the Cesar Diaz mod so you can switch it on or off.

—do I want him to jumper channels in some way?
No you want to separate them. You will soon be learning about not even using the Normal channels Preamp Tube.

— do I get him to do something with the input that reduces noise?
Remove the 68k input resistors that are paralleled at the inputs. Use switching jacks.

—are there any other aspects of the Healy mods I should get done?
Yes, but everyone has their own opinion as to what those are or are not, YMMV. Tuning an amplifier is like tuning a Hot Rod Engine. Some mechanics can just keep the engine running, and some can learn, experiment and figure out how to get every inch of power out of it. I say that to say this, you are chasing a dragons tail because there is no REAL concrete information on what is actually in Jerry's Twin amps. And that is what the inside GD circle want! They do not want the information to be made public. The ONLY thing i know is that it is NOT one of the Stock Twin circuits ever released by Fender! It is an adaptation/modification of one of them, they had them all! The only way i have found to get closest to his rigs AFTER the Wall of Sound tone is to modify the actual circuit of the Twin. The information shared with you is only the beginning of your journey. It is the beginning of your focus in on that tail. It will give you results you will feel and hear and inch you closer but in time, if your ear is really keen on nailing it, you will begin to hear and feel the things you are missing. And then the next part begins, Like Pointclear's journey! Or not, and then you will begin to settle with what you have or divert to what fits your situation. But if you can't keep the engine even running, then souping it up is out of the question. Some would rather take that route and take it to someone who might actually know what they are doing. It is an art! Not all techs know how to shape it, some only know how to change parts.

ya take what you need and ya leave the rest.
https://steelguitarforum.com/Forum11/HTML/004096.html


~waldo

[MikeMcA]

OMG Waldo, that link!

The amount of detective work that has gone into this is truly mind-boggling. That's 15 years ago!

Has anyone in the Dead organization ever said point blank that they don't want the details of Jerry's amp mods made public? Or is that inference? It's hard for me to understand the rationale for their secrecy.

I can only think of two scenarios: they plan to monetize it somehow, or they're trying to preserve a mystique around Jerry. The former seems unlikely at this point (although I'd happily pay for an exact repro of Jerry's twin and I bet I'm not the only one ) and the latter just seems...silly. So I dunno.

[Jblue76]

— .022uFs in the tone stack.
or .02uF MYLAR/POLYESTER

— non-inductive metal film plate resistors.
MIL SPEC RN Type use the 70's for the plates more robust.

—change all of the cathode resistors with military grade axial lead tantalum capacitors and do this for the bypass caps as well.
no ONLY the cathode bypass capacitors use Mil Spec CSR13 type

— do I ask him to disconnect the vibrato?
Have them install what is now called the Cesar Diaz mod so you can switch it on or off.

—do I want him to jumper channels in some way?
No you want to separate them. You will soon be learning about not even using the Normal channels Preamp Tube.

— do I get him to do something with the input that reduces noise?
Remove the 68k input resistors that are paralleled at the inputs. Use switching jacks.

—are there any other aspects of the Healy mods I should get done?
Yes, but everyone has their own opinion as to what those are or are not, YMMV. Tuning an amplifier is like tuning a Hot Rod Engine. Some mechanics can just keep the engine running, and some can learn, experiment and figure out how to get every inch of power out of it. I say that to say this, you are chasing a dragons tail because there is no REAL concrete information on what is actually in Jerry's Twin amps. And that is what the inside GD circle want! They do not want the information to be made public. The ONLY thing i know is that it is NOT one of the Stock Twin circuits ever released by Fender! It is an adaptation/modification of one of them, they had them all! The only way i have found to get closest to his rigs AFTER the Wall of Sound tone is to modify the actual circuit of the Twin. The information shared with you is only the beginning of your journey. It is the beginning of your focus in on that tail. It will give you results you will feel and hear and inch you closer but in time, if your ear is really keen on nailing it, you will begin to hear and feel the things you are missing. And then the next part begins, Like Pointclear's journey! Or not, and then you will begin to settle with what you have or divert to what fits your situation. But if you can't keep the engine even running, then souping it up is out of the question. Some would rather take that route and take it to someone who might actually know what they are doing. It is an art! Not all techs know how to shape it, some only know how to change parts.

ya take what you need and ya leave the rest.
https://steelguitarforum.com/Forum11/HTML/004096.html


~waldo

Thanks so much Waldo; I really appreciate the guidance! Inching closer will have to do for now, though I have no doubt that your right that my ear will eventually key in to some detail in the tone that isn’t quite there yet. As it stands now I’ve had to use a clean boost at the beginning of my chain (boost section of a Diamond J Drive— great pedal!) as well as a boost eq towards the end, using almost no added gain, boosting the mids and tilting the whole sound right over to the treble side. So maybe with a start on the mod journey I won’t need to run both of these pedals all the time.

One more question for you: can I/should I just pull v1 now before I get a chance to take the amp in to the tech for the other mods?

Thanks again, SO much! And Happy New Year!

[fatztreeboy]

i own a mid 70's twin.... w/ master volume...... the route i took was a differant road to rome..... the black facing is done, i say don't mod it all and just play it for 6 months... my amp had stock speakers and they sounded brittle sorta, harsh highs maybe.... so the only mod i did was buy two tone tubby red alinco's... 50 watts each... 100watts of leo tone into 100 watts of Marin County Weed Speakers.... they sound so smooth and make the highs more beefy n less schrill..... i read the post where u change out each part one at a time and then listen, seems like a huge leap of faith ... i doubt if the differences r that worth it.... Leo designed this circuit, jerry's fave circuit, i would just leave well enough alone and spend all that time practicing ur guitar modded twins lose their value , they already r amazing california amps . ... just play the damn thing

[waldo041]

One more question for you: can I/should I just pull v1 now before I get a chance to take the amp in to the tech for the other mods?

Thanks again, SO much! And Happy New Year!

You're Welcome and Happy New Year to you as well!

Yes, removing v1 is a simple and non invasive modification that you can do at home. Just pull out v1 and the voltages within the amp change and you will hear what that difference makes.

~waldo

[Jblue76]

So I spoke to my amp tech today and he suggested I buy the parts for the mods and bring them to him since he doesn’t stock those specific materials. He sent me to the digikey website. Shopping for this stuff as an electronics illiterate is, well, daunting. Couple questions for you experts out there:
1. For the tone stack they have polyester 0.022uF 225P series orange drops made by CDE, but there are three kinds each with a different voltage rating: 200v, 100v, or 400v. Which is the right one to buy, and how many of these do I need
2. I read a post on the steelguitarforum suggesting to replace the 250pF ceramic disc treble cap with a mica or even better polystyrene film/foil cap. Do I do this?
3. They have CSR13 tantalum capicitors, but what is the correct capacitance, tolerance, voltage and ESR to get?
4. What do I buy for cathode resistors and how many do I need?
5. I think I found the non-inductive metal film plate resistors on the website made by a company called Yageo but there are SO many different ones with different resistances and I don’t even know what the other differences are. (the mil spec RN type were recommended earlier in this thread). Is there a specific resistance I want? I’m not sure what the other differences are between them; they all say metal film for composition.

Thanks in advance! I really appreciate how generous everyone has been sharing info with me!!!

[lovetoboogie]

So I spoke to my amp tech today and he suggested I buy the parts for the mods and bring them to him since he doesn’t stock those specific materials. He sent me to the digikey website. Shopping for this stuff as an electronics illiterate is, well, daunting. Couple questions for you experts out there:
1. For the tone stack they have polyester 0.022uF 225P series orange drops made by CDE, but there are three kinds each with a different voltage rating: 200v, 100v, or 400v. Which is the right one to buy, and how many of these do I need
2. I read a post on the steelguitarforum suggesting to replace the 250pF ceramic disc treble cap with a mica or even better polystyrene film/foil cap. Do I do this?
3. They have CSR13 tantalum capicitors, but what is the correct capacitance, tolerance, voltage and ESR to get?
4. What do I buy for cathode resistors and how many do I need?
5. I think I found the non-inductive metal film plate resistors on the website made by a company called Yageo but there are SO many different ones with different resistances and I don’t even know what the other differences are. (the mil spec RN type were recommended earlier in this thread). Is there a specific resistance I want? I’m not sure what the other differences are between them; they all say metal film for composition.

Thanks in advance! I really appreciate how generous everyone has been sharing info with me!!!

For the Sprague Polyesters you only want 400v or 600v ratings...either will do...
Besides the 225p's you can also use 220's, 418p, or the 4PS or 6PS series. DO NOT use 715p or 716p series. Plenty of NOS polyester ones online for next to nothing ...

Example:

https://rover.ebay.com/rover/0/0/0?mpre ... 2588197894

For the preamp stages the cathode bypass resistor is unnecessary to change unless it has somehow drifted. They rarely do. The exception is the Reverb driver cathode resistor. Smart to upgrade this one to a 1W 2.2k ohm. Carbon comp is fine in this spot. If your Twin Reverb is a late model one you will want to retro-mod the reverb circuit back to AB763 specs.

Its the cathode bypass capacitor that gets upgraded to tantalum. For those you can use this one...

https://rover.ebay.com/rover/0/0/0?mpre ... 1549290136

For the 250pf treble cap either Mica or polystyrene are fine. I have had great results with the polystyrene's in my builds. Be mindful that small value Mica caps as of late have been failing left and right in current builds. Something about the latest batch of Mica base material. Plenty of chatter about it. Look for some NOS ones if you go that route.


Since Healy has spoken the gospel about non-inductive metal film resistors I have to believe that he misspoke. The only true non-inductive resistor is metal oxide. Metal film by design offers a measurable inductance(Ls).
* Edit: Ohmite seems to offer a "non-inductive" metal film but they are rather large in the 100k value. Would be very curious if Healy really used these.

It is good practice to over-rate these if you are going with Metal Film. Dale RN70's or TRW are the only metal films I would use personally. Plenty of them online.... They are super hi-fi and whisper jet quiet! Make sure you use 100k ohm... You will need one single 82k ohm for one the PI plates.


As a side note I see that you have referenced .02uf for your tone caps... Not to take away from all of Mike's hard work and super helpful direction...but Garcia's 75' Mesa Boogie was all stock. I have not seen his Twins so I can't speak on the likelihood
of the tone stack values. The Boogie had .1uf for Bass, .047uf for Mids and 250pf ceramic disc for the treble... The interest in converting the mid and bass caps to .02uf has not convinced me personally. But I am only one tech... A fun and useful mod that the pedal steel cats swear by is a slope resistor mod. This change will achieve a perceived bump in the mid and high mids, and also allow you to push the volume a little more on a stock Twin. You can make this switchable with a mini toggle or some such push pull on the front panel. If you are asking me, which you aren't, I would leave the tone stack cap values stock...and then see what you hear....

Hope this helps!

[Jblue76]

Is it good to use for the reverb driver cathode resistor a carbon film 1W 2.2K ohm cap versus a carbon comp cap?
Also for the treble cap I don’t see 250pF available in the polystyrene, just 220pF or 330pF. Is one of these the correct value?

[Jblue76]

Still shopping parts for the mod to the twin...

Do I just need two orange drops, one for bass and one for the mids?

How many of the 100k ohm metal film resistors do I need?

Also still wondering if I found the right part for the reverb driver cathode resistor— it’s a carbon film 1W 2.2k ohm. Carbon comp was suggested to me but I couldn’t find one with the correct values on Mouser.

And for the treble cap, the polystyrene is available in 220pF or 330pF, wasn’t sure which is the right one to replace the 250pF ceramic one.

Thanks so much out there!
J

[waldo041]

Knowing what parts are needed and how and where to order them is a skill a tech should be getting paid to take care of for you! The instructions and schematic you have been given already have all the information you and your tech need. If you are going to pay him to install them, he really should be doing the part ordering as well.

~waldo

[Jblue76]

I hear you, and I don’t disagree. He’s a good tech but not a Jerry guy, and at the end of the day I just want it done correctly.

I don’t have a schematic to show him. I’ve had a couple message issues lately I think. Did you send one?

[waldo041]

a twin reverb schematic.

correctly?

no one knows what was actually in his Twins except a handful within the GD circle. There are some techs here who have gone through some extremes to get the unverified information that is available and some of that has been shared with you. Some techs here have also gone to their own extremes to patent pend their own circuit since the GD refuses to release any information pertaining to Jerry's rigs.

Regardless if your tech is a Head or not, swapping a few components and values as well as ordering the parts needed for the work should not be out of his league. If it is, i would find a new tech!

~waldo