JTM45 vs. 5F6-A Bassman project

[TubeGeek]

Wow this circuit has tone up the wazoo!  I am in tone heaven.

Built from a mojo kit with some changes to the way I like to do things.

This one is staying in my collection.

It's paired up with a 4x12" cabinet loaded with Celestion Greenbacks, marshall cane grill cloth.

[SILVERGUN]

 

Nice stuff there TG.......glad to see your having fun up there in the new house, and it's not getting in the way of your work

 

[TubeGeek]

Nice stuff there TG.......glad to see your having fun up there in the new house, and it's not getting in the way of your work

 

Definitely having some fun here!

Thanks!

[plexi50]

I need to build another JTM 45. It's been at least over year or so. I think 
They just exude love beams. Or is that waves? 

[super&plexi]

looks sweet from my view. one question....are these 45s just stupid loud?. I have a factory JTM 45 w factory efx loop, plexi front, el34s, (in snakeskin...HA!), and maybe it's the tolex..., but holy cow, this thing is an in your face, undeniable presence. I've got a metal panel 72 super lead, and JCM800 50 watt Cameron modded head, but that small box 45 carries a big stick. I've taken to using those yellowjaket/GT tube sub things for el84s.( I have both brands, no discernible diffs.) just to get it tamed a bit. Are they all  super loud, & punchy, or are there differences..,metal vs. plexi, ...and are these "bluesbreakers"?.  respectfully _ LT.     oh yeah, I've been around here almost a couple o yrs, but computers aren't my bag, so I'm pretty sure I've introduced myself, but really can't be sure. if not, maybe I've been giving all of tubeNit, sluckey's, & kagliostro's, et al. props to Martha Stewart, or some cooking channel, hopefully not. again, thanx to all, & much R.E.S.P.E.C.T...LT

[TubeGeek]

Yes they are stupid loud.  That may not be practical for a gigging musician, maybe a 6v6 version would tame it down.  There are plenty of those variants out there.  

I chose to build this particular amp because I wanted an amp to match up with my Les Paul, SG and Strat mainly.  I want the classic rock tone that is so well known and liked.  For me, I had all the ingredients (ie. empty 4x12 cabinets that need to be used) so I figure'd why not.  I just played it for 20 mins and when finished my ears had a slight ring.  IT IS LOUD.  I had the bright channel vol at about 5-6.  Nice crunch.

I don't gig. I use these amps to play around occasionally and record jams/ideas.  I am building ribbon and condenser microphones and recording a few band projects per year too, I need something to record and have around for studio sessions.  They will not leave my music room unless I am convinced to sell and then I'd rebuild it anyways.

I recommend ear plugs or even noise cancelling headphones when jamming loudly.

Oh and welcome to the group, there are some good fellas here.

Added a new nameplate today...

[jojokeo]

I like the music room! What tubes are you running in the JTM? Is that an ukulele I spot up against the wall in it's little tweed case???

[Ed_Chambley]

Mojo kits are nice to build.  I have one of these, but it seems not loud.  I could not get much in the way of highs with the stock arrangement from Mojo.  I have split the cathode on v1 to have jtm 45 on the normal and plexi values on high.  Still if I get much over 2 on the bass it is very bottom heavy.  Also, mine seems to not want to play clean at all.  I normally have it connected to a 2 12 cab.  The original I have which is tubed with EL34's does have that cool marshall swirly clean, but I have never been able to get this one to do it.  If you play it ever so lightly with single coils with bass on 2 and mid on 2 and treble almost dimed it will get fairly clean, but if you dig in it will break-up.

I have replaced the rectifier with SS plug-in.  Reduced cap values, but still no clean.  The only real mod is a LARMAR PPMIV master.  I have a super nice OT I was planning to try.

If you guys know or have any idea of how to make the tonestack achieve more upper mids and highs, let me know.  I am considering raising the voltages.  I am using Mullard EL34's fx2's.

Did you get voltage readings after it was running?

[TubeGeek]

I like the music room! What tubes are you running in the JTM? Is that an ukulele I spot up against the wall in it's little tweed case???

I am in the process of deciding which tubes to leave installed.

I am auditioning JJ's, T.A.D.'s, EH's, Tung-sol's and Mullards (re-issue).

And yes that is a ukulele tweed case for one of my uke's, actually I use that case for my resonator uke!

[TubeGeek]

Mojo kits are nice to build.  I have one of these, but it seems not loud.  I could not get much in the way of highs with the stock arrangement from Mojo.  I have split the cathode on v1 to have jtm 45 on the normal and plexi values on high.  Still if I get much over 2 on the bass it is very bottom heavy.  Also, mine seems to not want to play clean at all.  I normally have it connected to a 2 12 cab.  The original I have which is tubed with EL34's does have that cool marshall swirly clean, but I have never been able to get this one to do it.  If you play it ever so lightly with single coils with bass on 2 and mid on 2 and treble almost dimed it will get fairly clean, but if you dig in it will break-up.

I have replaced the rectifier with SS plug-in.  Reduced cap values, but still no clean.  The only real mod is a LARMAR PPMIV master.  I have a super nice OT I was planning to try.

If you guys know or have any idea of how to make the tonestack achieve more upper mids and highs, let me know.  I am considering raising the voltages.  I am using Mullard EL34's fx2's.

Did you get voltage readings after it was running?

Interesting.  As this is a new amp to me I am still learning it's tone and I am experiencing the same as you describe.

In playing last night I did find that I couldn't dial in the clean tone I expected and the normal channel seemed darker than I expected.  I do think mine is loud though.  I haven't tried a strat yet, only a les paul.

I'll be tweaking and experimenting with the circuit too.  I have full voltages measured of course, I can post them later tonight when I get home.  It'll be open on the bench while it's being tested.

[plexi50]

TAD & TungSol power tubes sound real good to me and look well made. The TungSol preamp tubes sound good to but sometimes they wont read out on my tester. I think it's a matter of different prodution runs. Some do and some dont

[SILVERGUN]

I have split the cathode on v1 to have jtm 45 on the normal and plexi values on high. 

Ed,
Did you double the cathode resistor value to make up for it being split?
i.e....  If it said 820R for a shared cathode resistor on V1,,,,then when you split it, you should increase both to 1.5K to keep intended stock value

As is,,,if you put 820R in both positions, that would partially explain why it won't clean up.....lots 'o gain....and lots of gain boost in the low end due to that crazy high cathode cap value (250uf?)

[Ed_Chambley]

I have split the cathode on v1 to have jtm 45 on the normal and plexi values on high.

Ed,
Did you double the cathode resistor value to make up for it being split?
i.e....  If it said 820R for a shared cathode resistor on V1,,,,then when you split it, you should increase both to 1.5K to keep intended stock value

As is,,,if you put 820R in both positions, that would partially explain why it won't clean up.....lots 'o gain....and lots of gain boost in the low end due to that crazy high cathode cap value (250uf?)

I will check.  I used values Sluckey proposed.  Been a while since I have been inside of the amp, but intend to soon.  Each cathode has it's own bypass cap/resistor.  Cant remember.  Use a jumper patch to blend both.  It is like the attachment on v1.

Other values are different tho.  More consistent with the JTM 45.

[SILVERGUN]

If it's just like the Ceria. layout.......the least I would do is raise the 820R to a 1.5K (2.2K for even more clean) and lower the bypass cap value to like 10uf

That combination might also get rid of some of the boominess in that channel   

[TubeGeek]

Went home for lunch from my real job at noon cause I was curious if I could get good clean tones with a strat.  Yes, it's the clean tone I was hoping for!

I've never enjoyed the clean tone from my les paul.  That's a guitar I use for crunch mostly.


The fender 5f6-a uses a 12ay7 in v1 position, that may clean it up to where you like???

[jojokeo]

If you guys know or have any idea of how to make the tonestack achieve more upper mids and highs, let me know.

Try replacing the slope res to 100k, the cap to Treb/Bass to .047uF, and the other to .01uF.

[jojokeo]

Went home for lunch from my real job at noon cause I was curious if I could get good clean tones with a strat.  Yes, it's the clean tone I was hoping for!

I've never enjoyed the clean tone from my les paul.  That's a guitar I use for crunch mostly.

High output humbuckers vs low output single coils do that. Plug the Paul into the low gain input if you want more clean or the most you can hope for.

[TubeGeek]

Went home for lunch from my real job at noon cause I was curious if I could get good clean tones with a strat.  Yes, it's the clean tone I was hoping for!

I've never enjoyed the clean tone from my les paul.  That's a guitar I use for crunch mostly.

High output humbuckers vs low output single coils do that. Plug the Paul into the low gain input if you want more clean or the most you can hope for.

Yep

[punkykatt]

TAD power tubes??? They sound good they look good. In the past six months I have had 2- pair of 6V6`s go south in my home built tweed deluxe amp. Of coarse it happens at the gigs. The amp is biased cool at 70% mpd.  The tubes become extremely un matched. (low power and distorted sound) The last pair was just past the 90 day warranty.  Im not spending any more $ on TAD power tubes. I just cant trust them to last.  I built the amp in 2002 and I never had any problems until I started using the  TAD`s   Sorry for the rant.

[plexi50]

I have a pair of the recreated RCA black plate 6L6GC TAD tubes and so far they have held up for me. The layout for V1 split cathodes is all i have ever liked. You get a real nice blend of tones between the Normal & Bright channels. Here is the thunder tweaks layout/

[TubeGeek]

I have a pair of the recreated RCA black plate 6L6GC TAD tubes and so far they have held up for me. The layout for V1 split cathodes is all i have ever liked. You get a real nice blend of tones between the Normal & Bright channels. Here is the thunder tweaks layout/

Yes those tubes are nice! I've been using them for the past few 5f6a bassman's I built.  The 6L6WGC-STR.

I haven't tried the TAD EL34's until now.

I'm going to experiment with some mods now.

[super&plexi]

reply to queries;IOW... this circuit 'CAN' sound good w/dare i say, and don't castigate me to the SS pages, Chinese pre amp tubes. not PwrA, but preA. and a 12at in PI can sound good too. not micro-phonic of course, they just don't have to be lg. plate RCAs or whatever. that being said, i also like Brimar, and Amperex, but so cost prohibitive for me that I take em out for most of the time, only using to record, or special gigs( i know it's LAME). also, the cane grille really sounds great on these w/4x12 greens. cuts highs in a pleasing manner. . And props to bright cap mention-that thing must be a throw back to days when bass player, guitar(s), AND vocalist plugged into these. If running pedals,like I do, dirt especially, these are my settings:  bass, & mids maxed, treble and presence on 0, jumpered/or not, they seem to interact w/each other  channel wise,  but plug in to the brighter of the low, or the less bright of the high channel, and both volumes up, & take some names, 'cause the butt will have already been kicked. feel free to reply,or not. but above most all, (save family, friends, the dog, neighbors, & whatnot), CRANK THAT SUCKER UP, & enjoy they really are a great sounding circuit, in most all of their various incarnations, & incantations. thumzup!   L.T. 

[nandrewjackson]

Nice!  Very cool, indeed.

I was wondering,

I've never played through one of these,

Do they respond well with a Fuzzface or a Tubescreamer type circuit in front?
Or does that take away some of the guitar-to-speaker response and make it dull?

[TubeGeek]

I spent some time experimenting tonight, thanks for the ideas to try.  I decided to split the v1 cathodes and have the normal channel use the 820/250uF and the bright channel now has a 2k7/.68uF configuration.

I also tested between the JJ and TAD power and rectifier tubes.  I am not sure which I like yet. Plenty more tube auditioning will happen before I settle.

Right now I have the JJ's installed while I am going to "voice" the circuit.  

I can hear the changes with splitting the cathodes...I can't explain it yet because I realized after the fact I forgot to change impedances to 16 ohms when I played through the 4x12.  My test bench speaker cab has a vintage 30 8 ohm.  The amp was on 8 ohm all tonight.

So...I'll get back at it tomorrow with a fresh set of ears.

In the meantime I have been keeping track of voltages:

[TubeGeek]

Nice!  Very cool, indeed.

I was wondering,

I've never played through one of these,

Do they respond well with a Fuzzface or a Tubescreamer type circuit in front?
Or does that take away some of the guitar-to-speaker response and make it dull?

Good question...I'll let you know what I hear when I get a chance. I have invited a good buddy over to record some clips in the next day or two.

[Ed_Chambley]

If it's just like the Ceria. layout.......the least I would do is raise the 820R to a 1.5K (2.2K for even more clean) and lower the bypass cap value to like 10uf

That combination might also get rid of some of the boominess in that channel   

I have tried.  It is easier to change the cap.  With a 12Ax7 I have actually tried many bypass configs.  I am very familiar with what you speak, and agree in most cases.  If not using the normal channel at all, I still have the problem.  Last time I was in it, I found some plate resistors which had drifted.  That boominess you speak of is the JTM 45 tone.  It is present in the original.  Not as boomy as it seems on paper.  Back then we used treble boosters or if you wish a dallas rangemaster.

Thing is a JTM 45 with El34's does not have the wattage, so it suffers using a 100 watt cabinet.  There is something going on with the tonestack, but I also wanted voltages from TG's build.  I am simply going to change it to a 50 watter as I think the JTM 45 stock is about 36 watts or so.  Since I have put a plugin ss rectifier, I may increase the filter cap values.  The tonestack will begin overdrive about 12 oclock with any pot.  I do not like the Presence sweep either.

I am looking to get a clean from buckers.  My idea of clean may vary a little from yours.  It is easy to get
overdrive from an amp, but getting Two Rock clean is a different story.  I did not write nice overdrive.

The amp is loud compared to little amps, but not near as loud as a JCM 800.  When I wrote it wasn't loud, I was comparing it to other Marshalls, not a Deluxe.  I built this amp while doing other projects and have not spent much time tweaking.  That being said, I have an original and an original plexi.  The direction I am going with it is I have a new Heybour OT, 50 watt (copy of the Drake winding) I am going to install as I think the OT from Mojo is saturating, well I know it is.  I will get it, no problem.  I just wanted a voltage basis to refer to since mine have changed and also find out what others have done.  I also plan to use some relays to make Doug's hotswitch and a couple of other tricks to make it 2 channel.

IMO, a 5751 sounds best in a Bassman in v1 and it is fine in this JTM 45, but a JTM 45 never had EL34, the distortion is coming from the preamp.  I want it to be HiFi sounding and then hit a footswitch and get nasty.

I have friend that lives at the Metro forum who has done this, but he had lots of help and really is just learning so he doesn't know what he did.  Someone else helped him and he did not record the changes.  I played the amp, but I did not open it up.  Anyway, I will get it.  I was just curious how TG's turned out.

It is really a crazy idea to want a clean Marshall, but I have a 100 watt superlead which has the most beautiful clean tone.  SG, thanks for your input.  All comments help and get me thinking. 

[SILVERGUN]

SG, thanks for your input.  All comments help and get me thinking. 

No problem sir.......and sorry for the partial hijack TG   

Nice thread about an amp I look forward to building someday....and you guys do a great job of describing it's character

I only know about the split resistor value change from watching a Gerald Weber video about 6 times in the last 6 months,,,and thought I should share that "rule of thumb" in case you overlooked it

Every time you guys type I learn something new and I really appreciate that 

[jojokeo]

Ed, I think you're right on with your suspicions as fender pushed high voltages & stout iron for his clean tones, that was his main priority

[TubeGeek]

SG, thanks for your input.  All comments help and get me thinking. 

No problem sir.......and sorry for the partial hijack TG   

Nice thread about an amp I look forward to building someday....and you guys do a great job of describing it's character

I only know about the split resistor value change from watching a Gerald Weber video about 6 times in the last 6 months,,,and thought I should share that "rule of thumb" in case you overlooked it

Every time you guys type I learn something new and I really appreciate that 

No worries on hijacking.  I like it.

[TubeGeek]

Made a few changes to the circuit tonight and recorded some tracks for reference along the way of tweaking.

 changes:  normal channel added 250pF bright cap.  Bright channel with 120pF bright cap, separated v1 cathodes with .68/2k7 on bright channel. Increased nfb resistor value to 56k.

https://soundcloud.com/glacier

[floyd]

Whats' really groovy about the JTM45 , is , you can act and sound like a 16 year old boy  , and play idiotic classic rock , but that wears thin after awhile.

[TIMBO]

You guys make me SICK, you build great amps and can play as well  Good stuff 

[Ed_Chambley]

Made a few changes to the circuit tonight and recorded some tracks for reference along the way of tweaking.

 changes:  normal channel added 250pF bright cap.  Bright channel with 120pF bright cap, separated v1 cathodes with .68/2k7 on bright channel. Increased nfb resistor value to 56k.

https://soundcloud.com/glacier

I like the tweaking.  Amp sounds nice and very familiar.  I finally used a 100k pot for the nfb.  Gives the ability to have greasy bass tones when set low and gets focused and tighter as you increase.

Thanks for posting voltages.  I am working on a build and next I am going to give mine some attention.  Your voltages are almost exactly what I recorded as original voltages.  I have heard these amps called 1 trick ponies, but those comments usually come from people who don't know where the volume knob is on their guitar.  They make great blues and rock amps, but I use finger style pickin and it can get messy sounding.

Your strat sounded very Jimi.  Great work and thanks for sharing the clips.

[plexi50]

You guys make me SICK, you build great amps and can play as well   Good stuff  

The best of both worlds. I know your lovin the split cathode arraingment. Sounds great! Nice tonal changes.  

[SILVERGUN]

Really great demos of that amp  ....very "classic" sounding,,,a real keeper

Thanks again for sharing it all

[rzenc]

Congrats TG!!!! Amp sounds super!

Best Regards

R.

[tubenit]

Loved the strat tone and especially the playing thru the amp!  Great job on your amp.

A thought for you  ............. on the cathode with the 250uf,  try a 10uf or 5uf there sometime. I have found values lower than 22uf to be significantly more transparent in my amps in the preamp. The larger values sound somewhat muddy to me and your guitar can't use the "250uf frequency range" anyway.  You will still hear a big contrast between 10uf and .68uf.

With respect, Tubenit

[Ed_Chambley]

If you guys know or have any idea of how to make the tonestack achieve more upper mids and highs, let me know.

Try replacing the slope res to 100k, the cap to Treb/Bass to .047uF, and the other to .01uF.

Duncan says you would be correct.  The slope is 56k.  I was under the impression raising the slope resistance would attenuate the highs.  Do I have it backwards?  I get the idea and it makes very good sense.  Thanks.

[jojokeo]

Yes, and mids won't be quite as scooped in the same range compared to Marshall's values.

[plexi50]

Loved the strat tone and especially the playing thru the amp!  Great job on your amp.

A thought for you  ............. on the cathode with the 250uf,  try a 10uf or 5uf there sometime. I have found values lower than 22uf to be significantly more transparent in my amps in the preamp. The larger values sound somewhat muddy to me and your guitar can't use the "250uf frequency range" anyway.  You will still hear a big contrast between 10uf and .68uf.

With respect, Tubenit

I find that the lpwer values really add a perfect bass pitch that is not over whelming and just the right spice for many amps. In the begining for me it was all 330uf and then 250uf. But then i discoverd that even a 2.2uf and 4.7uf would still add bass but in a more articulate way. I wouldnt have not believed it had i not tried lower cat cap values.

[Willabe]

Hey I just listened to your sound clips. Really good!     

The amp sounds great, plus ;

Your tone and rhythm chops/chords and your timing on the strat Jimi kind of things were especially good, IMO. Free flowing yet solid and very nice use of open strings with the moving chords.

Well done!     


                  Brad     

 

[DummyLoad]

sounds really nice. great work!   

--pete

[g-man]

Deleted

[Ed_Chambley]

I built the same Mojo kit several years ago and left the JTM45 stock values, except I gradually lowered the 250uF V1a bypass cap to 100, 47, 25, 10 and finally 4.7uF. Early on I tried EL34's (when it still had the 250uF bypass cap) but switched back to 6L6's pretty fast. I'm thinking about trying EL34's again and do the split cathode on V1. For those of you that have done the split cathode, did you also add another 0.68uF bypass cap on V2a like the Plexi50 circuit? Thanks.

I have tried this arrangement along with others.  It had a fairly large bass hump and did not sound like I expected.  Pure vintage.  Great tone, but I like a little more variance in the tone.  To tell you the truth, I currently have no idea what is in my Mojo JTM 45 right now, but I can assure you when I get back to it I will be able to get 60's, 70's and 80's Marshall tones with it with a kicker.  Not sure how I am going to do it, but I am going to get a clean tone as well.  I have a good idea how.  Time is not on my side, but eventually I will get to it.

[TubeGeek]

Still tweaking things...

Recorded new clip using a Telecaster and a ribbon microphone

It's the recognizable tone we all know!

https://soundcloud.com/glacier

[jojokeo]

Sounds good, what speakers are you running in your cab?

[TubeGeek]

Sounds good, what speakers are you running in your cab?

This is with a 4x12 loaded with Celestion 25W greenback's.

[Ed_Chambley]

I finally got around to doing more tweaks on my Mojo JTM 45.  First I replaced the OT with a Heybour HTS-5122 which is wound like a Drake 784-139.  The 16 lot price is $64.90.  They will sell one for this if you ask.  The difference is huge, open tone.  Next I reduced the first dropping resistor from 10K to 5K which increased voltages to the preamp and checked it with a GZ34 and SS rectification.  I liked both, so I made it switchable and biased for SS.

I built the amp about a year and half ago and most of the resistors had drifted an unacceptable amount.  They were the 5 band metal film resistors.  Using values for the tone stack JoJo suggested, I changed the slope to a 100k, the cap going to the treble/bass is now a .047 and to the mid a .01.  I did not lose any of the beloved Marshall tone, but gained a much more useable tone stack.  The middle now has much more gain and the upper mids are smooth, nothing harsh but yet still bright with a les paul bridge.  I can still get a great woman tone with the normal channel and plexi tones from the bright.  Jump the channels and loads of variety.  Changed the Phase Inverter Coupling Caps to .033 and everything else is the values of the layout posted.  The super plexi layout.

I changed the bypass values on v1A, but went back to stock as I lost the dark jazz tone.  All the caps are now sozo vintage yellow except anything to do with the tone stack.  These are the blue sozo.  Tried upping the filter caps to 50uf to 32uf, but went back to stock as it became a little stiff.  Not very noticeable except when playing double stops they did not have that hair of breakup I like.

Kept the LarMar master as it is great in this amp.  It is loud as hell now.  I pulled out my best stash of tubes and ended up with Mullard FX2, EL34 for power and a Mullard GZ34.  In the PI I have a nicely balanced new Tug-Sol.  I like this tube in all of my amps that call for a 12AX7 in the PI.  In v2 I have a Smooth Plate Telefunken and in V1 a NIB Sylvania.  Tried a Mullard and RCA Blackplate here, but it sounded best with the yellow ink Sylvania.

It was very surprising.  I expected to make compromises with changing the tone stack values, but there were none.  I am very pleased as it is now a very versatile amp.

[SILVERGUN]

Still tweaking things...

Really sounds great and just makes me want to play guitar....great recording quality

I finally got around to doing more tweaks on my Mojo JTM 45.

Thanks for taking the time to share all that......
The coolest part about this "new" hobby to me is feeling empowered by the idea that I can just wake up one day and decide to build a little piece of history.......and all of this research makes it a lot easier to decide "what piece of history?"....and what puzzle pieces to use 

[TubeGeek]

Still tweaking things...

Really sounds great and just makes me want to play guitar....great recording quality

I finally got around to doing more tweaks on my Mojo JTM 45.

Thanks for taking the time to share all that......
The coolest part about this "new" hobby to me is feeling empowered by the idea that I can just wake up one day and decide to build a little piece of history.......and all of this research makes it a lot easier to decide "what piece of history?"....and what puzzle pieces to use  

The recording path on the tele clip is:  amp to Nady ribbon mic (not too shabby eh?) into a seventh circle diy N72 (neve clone/style) mic preamp. From the mic pre the signal goes to an Apogee Ensemble A/D converter and finally into Logic recording software.  I mixed a little light compression with a puig-tec Fairchild 660 , a little rolloff on low end and slight boost at 5 kHz with puig-tec eqp1-a plugin and finally a hint of reverb just to add spice.  Mogami 2549 cabling used.

I feel like I am studying history right now!  I have just finished building a 5f6-a bassman yesterday.  Now that I have built the jtm45 and 5f6-a and they are fresh in my mind, I am going to study them side by side.  I have the Richard Kuehnel book on these amps to help me expand my horizons.  I have multiple sets of preamp, power and rectifier tubes to audition too. In fact that is where I am in the project at the moment.  

I built a 5f6-a about this time last year and that was purchased by a guy that I am hiring to build custom hardwood cabinets every so often for me.  His amp had metal film resistors, my new amp has carbon comp's.  I am going to put all 3 side by side and analyze them closely.  I just love this hobby.

I love seeing amp pics on this forum so I am sharing these...