Front and back:
Guts (power section complete minus snubber cap which is on its way (thanks Brian!!)):
JTM 45/100 build progress - Photos
Moderator: VelvetGeorge
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gtomax
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- Joined: Thu Jul 28, 2005 4:20 pm
- Location: Los Angeles
JTM 45/100 build progress - Photos
I've been asking so many questions here I thought I'd change it up and just post a thread with pictures of the build progress. Everyone loves pictures!
Front and back:
Guts (power section complete minus snubber cap which is on its way (thanks Brian!!)):
Front and back:
Guts (power section complete minus snubber cap which is on its way (thanks Brian!!)):
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shakti
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- Joined: Tue Apr 05, 2005 9:06 am
- Just the numbers in order: 7
- Location: Ramnes, Norway
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Billy Batz
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shakti
- Senior Member
- Posts: 2053
- Joined: Tue Apr 05, 2005 9:06 am
- Just the numbers in order: 7
- Location: Ramnes, Norway
OK, so that's the same board material George carries?I was unsure if that was perforated like in the shots, but if it it will work fine for me. I'm not so picky about whether or not it loks exactly like the more brownish stuff used originally as long as it's on the inside of the amp. I'm extremely picky about exterior cosmetics, though...
Still looking for the perfect JTM45 front and back panels, so if anyone has any tips...
Still looking for the perfect JTM45 front and back panels, so if anyone has any tips...
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gtomax
- Senior Member
- Posts: 259
- Joined: Thu Jul 28, 2005 4:20 pm
- Location: Los Angeles
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gtomax
- Senior Member
- Posts: 259
- Joined: Thu Jul 28, 2005 4:20 pm
- Location: Los Angeles
Update: It's all done! I'll have pictures tomorrow hopefully of the guts. I have one possible problem. The amp is not LOUD. I mean, it's loud, but it's not LOUD. On 10 it's probably about as loud as my Hiwatt DR103 on 3 or 4 or my 63 Fender Bassman on 5 or 6. Also it's pretty clean sounding. I was thinking that the clean sounding (nice crunch but you really gotta bang on the strings with the thing on 10 and presence all the way up) would burn in and it'd give up the distortion like on Flames' build. The volume though seems weird.
It's a 4xKT66 amp biased at 40ma. At first I thought the bias was off because at 5 it was downright quiet. I was right... the bias pot was wonky. When I was mounting the bias pot, I tried to do it the new way George described in the repairs/mods section with soldering the side tabs to the turrets to make it more secure. One leg went to the bias capacitor and the other leg to the 56k resistor. Well the problem was that the side tabs didn't stick to the turrets and I think something got messed up inside the pot. When I checked the bias it was down around 16ma. When I would press down on the pot the reading would jump up to the normal 40ma. So I soldered two little legs of buss wire to the side tabs and then to the turrets and everything seemed better, biased up reliably to 40ma. The amp was in fact louder, but still seemingly not normal. Tone is pretty good, no weird pops/fizzes/noises etc. just the fact that it's a pretty clean sound and not that LOUD. The 150k resistor seemed high compared to other models and the 56k also. My amp is set up with these values just like the layout with the addition of the bias pot going with one leg on the right bias cap and left leg having the 56k resistor connected to it. Is that correct?
I will take pictures tomorrow as I know this is kind of useless without pics to troubleshoot, but does anyone have any ideas offhand? Attached here is the layout so you can check it out. The only changes from this layout are the bias pot, the lar/mar MV which works perfectly, and the preamp cap is a 20uf instead of a 32uf. Bias was set with the MV all the way up.
Incidently there is zero ghosting in the amp so far...
The layout also doesn't show grounding scheme. It is as follows: Mains, screen and PI filter caps and PI pot to one ground point. All grounds from main board except V1 cathode to pot buss, then pot buss to ground point. V1 cathode and inputs to third ground point.
NFB is 47k on the 8 ohm tap, transformers are Marstran 1202-84 and 1203-43.
It's a 4xKT66 amp biased at 40ma. At first I thought the bias was off because at 5 it was downright quiet. I was right... the bias pot was wonky. When I was mounting the bias pot, I tried to do it the new way George described in the repairs/mods section with soldering the side tabs to the turrets to make it more secure. One leg went to the bias capacitor and the other leg to the 56k resistor. Well the problem was that the side tabs didn't stick to the turrets and I think something got messed up inside the pot. When I checked the bias it was down around 16ma. When I would press down on the pot the reading would jump up to the normal 40ma. So I soldered two little legs of buss wire to the side tabs and then to the turrets and everything seemed better, biased up reliably to 40ma. The amp was in fact louder, but still seemingly not normal. Tone is pretty good, no weird pops/fizzes/noises etc. just the fact that it's a pretty clean sound and not that LOUD. The 150k resistor seemed high compared to other models and the 56k also. My amp is set up with these values just like the layout with the addition of the bias pot going with one leg on the right bias cap and left leg having the 56k resistor connected to it. Is that correct?
I will take pictures tomorrow as I know this is kind of useless without pics to troubleshoot, but does anyone have any ideas offhand? Attached here is the layout so you can check it out. The only changes from this layout are the bias pot, the lar/mar MV which works perfectly, and the preamp cap is a 20uf instead of a 32uf. Bias was set with the MV all the way up.
Incidently there is zero ghosting in the amp so far...
The layout also doesn't show grounding scheme. It is as follows: Mains, screen and PI filter caps and PI pot to one ground point. All grounds from main board except V1 cathode to pot buss, then pot buss to ground point. V1 cathode and inputs to third ground point.
NFB is 47k on the 8 ohm tap, transformers are Marstran 1202-84 and 1203-43.
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gtomax
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- Joined: Thu Jul 28, 2005 4:20 pm
- Location: Los Angeles
Fixed - it was a bad tube in V2. Thanks Russia... once I swapped for NOS bugleboys it fired up like a champ and is LOUD!!!!!!! With plenty of chunky overdrive on tap. It lives! I'm going to play it for a while and burn it in and then possibly lower the PI filtering.
What a fun project... pics to follow.
What a fun project... pics to follow.
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gtomax
- Senior Member
- Posts: 259
- Joined: Thu Jul 28, 2005 4:20 pm
- Location: Los Angeles
All complete - photo overview
Overview of chassis from back. Its friend is pictured in back, 1963/4 transitional Bassman.
Transformers are Marstran, chassis from top sitting on Mojo 1960B cab loaded with Scumback M75/H75HP speakers in X pattern.
20H RS clone choke
Naturally...
Overview of guts
Power Section. 50uf Mains filtering & 64uf PI Filtering are non-stock as well as the master volume added and the output jacks wired Hiwatt style.
Shot of the preamp main board. Non stock input wiring and you'll notice the empty ground lug. Failed attempt at star grounding, stock ground scheme runs much quieter in this chassis.
Closer shot of the preamp main board. Check out that honking V2 plate resistor! It's the only wattage I had
. Input grounding is routed non-stock because of previous attempt at grounding. Now it runs dead quiet. Also pictured 100pf bright cap and 47k NFB resistor.
Close shot of V1 tube wiring with socket mounted resistors. Honkin V2 resistor as well.
Detailed shot of MV and output jack wiring
Shuguang KT66 tubes for power, Delta code Miniwatt 12AX7s in V1 and V2, RCA Command 5751 in driver position. Mini Bulgin mains connector.
Finally the most important question: how does it sound?! FANTASTIC. It is dead quiet, great natural overdrive. Sparkling cleans with tons of depth and character! I think the M6 laminations help on that one. On CH1 vol 7 you got Angus. Back it off 1 and you got Malcolm. Change V3 to a new production tungsol 12ax7, strat with SD little 59 bridge pup and volume and presence up to 9 and you can get a pretty convincing Somebody Get Me A Doctor. My reverse headstock olympic white 60s strat is in the mail and I'm guessing a little piece of Jimi is in this amp.
In one word: Yahtzee!
Transformers are Marstran, chassis from top sitting on Mojo 1960B cab loaded with Scumback M75/H75HP speakers in X pattern.
20H RS clone choke
Naturally...
Overview of guts
Power Section. 50uf Mains filtering & 64uf PI Filtering are non-stock as well as the master volume added and the output jacks wired Hiwatt style.
Shot of the preamp main board. Non stock input wiring and you'll notice the empty ground lug. Failed attempt at star grounding, stock ground scheme runs much quieter in this chassis.
Closer shot of the preamp main board. Check out that honking V2 plate resistor! It's the only wattage I had
. Input grounding is routed non-stock because of previous attempt at grounding. Now it runs dead quiet. Also pictured 100pf bright cap and 47k NFB resistor.Close shot of V1 tube wiring with socket mounted resistors. Honkin V2 resistor as well.
Detailed shot of MV and output jack wiring
Shuguang KT66 tubes for power, Delta code Miniwatt 12AX7s in V1 and V2, RCA Command 5751 in driver position. Mini Bulgin mains connector.
Finally the most important question: how does it sound?! FANTASTIC. It is dead quiet, great natural overdrive. Sparkling cleans with tons of depth and character! I think the M6 laminations help on that one. On CH1 vol 7 you got Angus. Back it off 1 and you got Malcolm. Change V3 to a new production tungsol 12ax7, strat with SD little 59 bridge pup and volume and presence up to 9 and you can get a pretty convincing Somebody Get Me A Doctor. My reverse headstock olympic white 60s strat is in the mail and I'm guessing a little piece of Jimi is in this amp.
In one word: Yahtzee!
.