Need advice for a JTM45 build (improving a TAD kit)

[AndyD]

Just needs final assembly but it is Summer with lots of warm, dry garage jobs to do. As I have x4 projects at different stages (one particular waiting on 45/100 OT and choke) the others I’ve gathered the bits ready for winter or when it is too cold or wet to be outside ). So I just need a nudge to build or sell as kit.

 

[yossarian]

If it is of interest I have a JTM45 in embryo. Pihers mustards block end chassis ab cts pots, CT pt, can’t remember OT (Drake,Dagnal or Merren) I’m in Rome this week so would need to check. No headbox tho’

Sounds great! That's a very nice offer! Can you PM me when you get back with more details (what's included, what's missing, price, etc.)?

 

[yossarian]

Another question I have is if there's a way to have a more JTM45/100-ish sound with a JTM45 (especially on the cleaner side). I love the JTM45 sound but I have come across some amps that sounded too dark and almost muffled for my taste wheras others were very warm but still brilliant. I guess many people will say that a JTM45 is dark sounding but I've heard others. Which components play a role here? Is it down to certain specs, OTs, tubes,...?

 

[Chris-in-LA]

Thanks for the warm welcome!
Will the Valvestorm kit be the same as the MetroAmp kit? Just trying to understand: In how far is such a kit better than the TAD kit? Does one then freely choose between RS and Drake according to taste? I didn't know that one could directly order from Heyboer.

Valvestorm sells the parts for the Metro kit. Unfortunately, Heyboer has not been supplying George Metropoulos with their Metro-spec transformers for a while. So you’d have to get the transformers elsewhere. I use Amp Parts Direct for the transformers.

 

[Chris-in-LA]

Another question I have is if there's a way to have a more JTM45/100-ish sound with a JTM45 (especially on the cleaner side). I love the JTM45 sound but I have come across some amps that sounded too dark and almost muffled for my taste wheras others were very warm but still brilliant. I guess many people will say that a JTM45 is dark sounding but I've heard others. Which components play a role here? Is it down to certain specs, OTs, tubes,...?

Some of that might be due to the bright cap. Metro uses a 500pf and that amp is brighter sounding than the Ceriatone kit which uses a 100pf bright cap. You can play with the values there. I use the 500pf cap on both kits and they are now almost identical in tone and sound. I believe some guys go as high as 5000pf.

 

[playloud]

Another question I have is if there's a way to have a more JTM45/100-ish sound with a JTM45 (especially on the cleaner side). I love the JTM45 sound but I have come across some amps that sounded too dark and almost muffled for my taste wheras others were very warm but still brilliant. I guess many people will say that a JTM45 is dark sounding but I've heard others. Which components play a role here? Is it down to certain specs, OTs, tubes,...?

The JTM 45/100 is basically just a JTM45 with a doubled power section (as the name suggests). The early ones that used 2 OTs were quite literally that!

Side by side, you'll notice some extra bass and treble due to the Fletcher-Munson effect, plus extra headroom and harmonic complexity. There's also the differences in PT, which again increase headroom (very high B+ on some 45/100s), although that is offset in feel by the 'squish' of relatively lower filtering (16uf on screens, i.e. just 4uf per tube!)

I guess what I'm trying to say is that I don't think the JTM45 should be darker, per se, than a 45/100 - although there is plenty of room for variety in each category. It is hard to emulate the bigger power section, however.

Fwiw, I don't think my 45/100 clone excels at clean tones. It needs just a little bit of grit. The later (JMP) amps with stiffer power sections are better for pure cleans.

Some of that might be due to the bright cap. Metro uses a 500pf and that amp is brighter sounding than the Ceriatone kit which uses a 100pf bright cap. You can play with the values there. I use the 500pf cap on both kits and they are now almost identical in tone and sound. I believe some guys go as high as 5000pf.

The bright cap on 45/100 was the same as 45s (100pf), from what I've seen, but feel free to experiment.

I don't really like bright caps. They sound bad at low volume settings, and non-existent at high volume settings, so they really only 'work' in a narrow range of the volume pot.

There are other ways to make a JTM45 brighter, however. Lower cathode bypass cap (25uf instead of 330uf), 'lead' tone stack and 470k mixer resistors for a start. There's also the tone settings themselves (try rolling bass completely off) and the speakers. Hard for an amp to sound 'muffled' with alnicos!

 

[neikeel]

Pictures as it is.
If interested let me know, I would suggest me doing the build and testing etc.

As you can see I used modern selectors and an IEC mains inlet so that it should comply with modern safety standards. It is not drilled through the chunky alloy endblocks as I would not do that until the correct cab was located.

 

[Central Scrutinizer]

Pictures as it is.
If interested let me know, I would suggest me doing the build and testing etc.

As you can see I used modern selectors and an IEC mains inlet so that it should comply with modern safety standards. It is not drilled through the chunky alloy endblocks as I would not do that until the correct cab was located.

@neikeel built and tested an amp for me. It is amazing! Top-Notch stuff!

You should seriously consider his kind offer @yossarian .

 

[BlueX]

Pictures as it is.
If interested let me know, I would suggest me doing the build and testing etc.

As you can see I used modern selectors and an IEC mains inlet so that it should comply with modern safety standards. It is not drilled through the chunky alloy endblocks as I would not do that until the correct cab was located.

Really nice project!

 

[neikeel]

OP has other plans so I guess this project will wait until the weather changes and clocks go back in the Autumn.

 

[jesone]

OP has other plans so I guess this project will wait until the weather changes and clocks go back in the Autumn.

Is this still available?

 

[neikeel]

Is this still available?

As it’s still Summer time here yes.

 

[neikeel]

Update
Amp is finished, up and running and shaking the windows! Only quick i-phone pics:

No head cab yet.
Go the KT66s biased spot on 70% and with plate voltages of 470v she is pretty loud and gets pretty crunchy after 6 on the dial.
Going to soak and play over next few days to get bedded in.