JTM 45 OT Impedance

Blackburn · Post by **Blackburn** » Wed Feb 13, 2013 9:03 pm

I've looked around some and the general consensus seems to be using 8k historically, while 6.6k will yield a cleaner, more low end response with 5881s and KT66s. Correct me if I'm wrong because I know there was some mismatching going on. I have the RS triple primary including 3.4k. I don't plan on running EL34s because I don't think I will go for that sound, but 5881s and KT66s are a definitive yes. The secondary is at 8 ohms only so I won't be doing any mismatching with a cabinet.

Just curious as to everyone's opinions for which one may be preferred over another for different reasons.

David

Reeltarded · Post by **Reeltarded** » Wed Feb 13, 2013 9:22 pm

Exactly as you say. The 8k will be less linear, and the 6k6 will be notably cleaner sounding with more of the lowend that you'd get with a fenderish amp. some say too much. I wonder what the hell they are hearing.

Blackburn · Post by **Blackburn** » Wed Feb 13, 2013 9:52 pm

Okay cool. I'll go with 8k then. I plan on using a 220uf cathode cap on v1 and don't want an overflow of lows, especially since I play a LP. I'll definately try out the 6.6k just to experiment, but who knows, maybe that's what I'll dig with my LP. I did read that Clapton's BB Marshall was wired for 6.6k.

David

LeftyStrat · Post by **LeftyStrat** » Thu Feb 14, 2013 12:09 am

Don't shy away from at least trying the 3.4k with EL34's. That turned out to be my favorite with my jtm45, at least for a strat.

Blackburn · Post by **Blackburn** » Thu Feb 14, 2013 2:32 am

Yeah I may do that when I (eventually) buy some XF2s. I just always think of them with SS rectification and hotter pres. I guess I could always pop in the diode cap in the rect socket and make a .68 cap switchable on v1s cathode, with a bias adjustment of course, and then see how she do...

Actually that sounds pretty cool.

David

LeftyStrat · Post by **LeftyStrat** » Thu Feb 14, 2013 2:58 am

One of my favorite production amps is the Germino Club 40. I modded my JTM45 to similar specs. I used a tube rectifier, dropped the first cathode bypass cap to 5uf. Increased the preamp filtering to 32uf.

I just found the original JTM45 to be very woofy, undefined bass. I didn't want to go all the way to fifty watt specs. Just wanted something in-between.

Just keep in mind, my mods were for great strat sounds. It definitely takes it further away from the Beano tone.

Here's my favorite clip of the Club 40:

http://www.germinoamps.com/audio/tribute.mp3

Some clips with a Les Paul:

http://www.germinoamps.com/audio/club40/c40_ledzep.mp3

Reeltarded · Post by **Reeltarded** » Thu Feb 14, 2013 3:04 am

I always TRY to plan for the easiest form of awesome. I have a theory about simplicity and available parts so I not only like the 34s for the sound, they are endearing in their ubiquity. Even maw and paw have a pair of 34s over at ye locale music shoppe. KT66 not suh'much!

I also believe the tone is in the player. Your fingers know how to make your amp sound not so dirty.

Anything that a diode bridge or a tube choice will do can be tweaked around as well. I have made some wildly clean leaning Marshalls in the last couple years. I like SS rec because it costs twelve cents and it isn't likely to flash itself to death after moving AND it sounds good. heh

Oops! Wrong thread!

LeftyStrat · Post by **LeftyStrat** » Thu Feb 14, 2013 3:16 am

Reeltarded wrote: Your fingers know how to make your amp sound not so dirty.

I guess my problem is a strat into a JTM-45 with KT66's didn't have enough dirt. I guess my fingers aren't big enough

I will admit when I was messing with the JTM-45 circuit, the only production KT-66's at the time were chinese.

The other variable is I used a PT I bought from Paul Ruby that I think might have been too good or over-engineered for the circuit.

Sometimes bad is good.

At least that's what I keep telling the ladies.

ToneMerc · Post by **ToneMerc** » Thu Feb 14, 2013 3:17 am

Blackburn wrote:I've looked around some and the general consensus seems to be using 8k historically, while 6.6k will yield a cleaner, more low end response with 5881s and KT66s. Correct me if I'm wrong because I know there was some mismatching going on. I have the RS triple primary including 3.4k. I don't plan on running EL34s because I don't think I will go for that sound, but 5881s and KT66s are a definitive yes. The secondary is at 8 ohms only so I won't be doing any mismatching with a cabinet.

Just curious as to everyone's opinions for which one may be preferred over another for different reasons.

David

The 65' that I worked on had the RS OT wired for 8K and had almost 460V on the plates. So when I built my clone a few years ago, I used an 8K and it has 450V on the plates. Personally, for a straight JTM45 I prefer the higher voltage and the 8K tap. The 6.6K version and low plate voltage can get a bit muddy.

I like the JTM50(el34/3,4K version) with the softer voltages in the 415-420V range.

TM

ToneMerc · Post by **ToneMerc** » Thu Feb 14, 2013 3:20 am

Blackburn wrote: I did read that Clapton's BB Marshall was wired for 6.6k.

David

I don't think anyone knows for sure, as I've read that it was wired for 9K.

TM

LeftyStrat · Post by **LeftyStrat** » Thu Feb 14, 2013 3:31 am

ToneMerc wrote: The 6.6K version and low plate voltage can get a bit muddy.

TM, thanks for this. Might explain my experiences.

Reeltarded · Post by **Reeltarded** » Thu Feb 14, 2013 3:43 am

ToneMerc wrote: I like the JTM50(el34/3,4K version) with the softer voltages in the 415-420V range.

TM

Great rig! Hmm... second favorite! For no visible reason the tone controls really work well on those amps, better than other models... feels like.

The transitional with a tube rec is really an amazing thing.

ToneMerc · Post by **ToneMerc** » Thu Feb 14, 2013 3:58 am

Reeltarded wrote:
ToneMerc wrote: I like the JTM50(el34/3,4K version) with the softer voltages in the 415-420V range.

TM
Great rig! Hmm... second favorite! For no visible reason the tone controls really work well on those amps, better than other models... feels like.

The transitional with a tube rec is really an amazing thing.

I like the GZ34 JTM50 as well. Funny but some of my fav Marshall circuits are the ones that don't sound, "like a Marshall"

TM

Reeltarded · Post by **Reeltarded** » Thu Feb 14, 2013 4:07 am

Played 4 holers forever wishing for something that I couldn't get until I could do it myself. I do get what you are saying there.

That said, the one in a hundred that *is* the good one really IS good.. something alive in there.. let's poke at it with a stick and see what good comes from that! lol

groovtubin · Post by **groovtubin** » Thu Feb 14, 2013 4:28 am

Blackburn wrote:Okay cool. I'll go with 8k then. I plan on using a 220uf cathode cap on v1 and don't want an overflow of lows, especially since I play a LP. I'll definately try out the 6.6k just to experiment, but who knows, maybe that's what I'll dig with my LP. I did read that Clapton's BB Marshall was wired for 6.6k.

David

IF you have TOO much lowend with the 220uf, try lowering the V1 coupling caps instead, it produces a nice sound, my .02

jim

The Amp Garage

JTM 45 OT Impedance

JTM 45 OT Impedance

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coupling caps