JTM45 Build

[statorvane]

statorvane, who did those very nice looking cabs for you? Yourself?

Guilty as charged. Thank you kindly for the compliments.

Personally my hat goes off to those brave souls that work with finger joints and natural finishes. You can hide a lot of things beneath a wrap of vinyl. I'd love to try a tweed or blackface style 4 x 10" combo in natural ash. One of these days.

[Littlewyan]

Thats pretty awesome that you made those cabs yourself. When I show people my amps and they say wow it looks great, I then have to admit the cab was made for me . One day though! And yeah natural finish stuff would be difficult!

[Littlewyan]

Here is an update.

I've fitted the faceplates along with most of the hardware. I've done quite a bit of wiring and even used lace to keep it tidy.

One issue that has arisen is the rear faceplate sticks out of the bottom of the chassis by about 0.5mm. So when the amp is upright its resting on the faceplate and not the chassis. Unfortunately I stuck the faceplate on before I realized! So I may have to cover the bottom of the chassis with clingfilm and masking tape then use sandpaper on the faceplate. Although I do use 0.5mm thick aluminum for the shield in the bottom of the head cabinet so that might fill the gap enough so the amp rests on the chassis and not the faceplate. We'll see.

Anyway its coming along quite well and I'm having a lot of fun building it. Taking my time with this one and as a result finding it much more enjoyable. Be sad when its finished .

[joeboo88]

Wow that looks good.

[M Fowler]

Looks great.

I like Michael at Modulus products and he has great service too.

Mark

[norburybrook]

Looks great.

I like Michael at Modulus products and he has great service too.

Mark

michael was very helpful when I built my JTM 45 in supplying all the parts.


I would definitely recommend him to anyone.

@Littlewyan , I built mine with KT66's and it overdrives magnificently with plenty of mid and bottom and not at all harsh in the normal channel.

the clean sound is also superb in the high treble channel, chimey yet smooth.


here's mine finished with the 4x10 cab.

Marcus

[Littlewyan]

Looks really nice, where did you get the cab from?

I'll post update pics at the weekend. The amp is now near completion, I just need to finish wiring up the turret board, then I can fit the components onto it and then I'm done!

[norburybrook]

a guy called Chris Uff (got his details from amp maker in Cambridge)made the cab to my spec and I got the old Marshall plate from Ebay.




Marcus

[Littlewyan]

O yeah I always use Chris for my head cabinets. I didn't know he could do that sort of covering though! Looks smart. I might fit the small gold Marshall script logo to my cab.

[Littlewyan]

I've been a bit silly and decided to follow Metroamp's layout without thinking and I wired the reservoir capacitor on the cold side of the standby switch. Now it would be a bit of a wiring nightmare to move it to the other side so my thoughts are:

1. Do what Roe said and put a 100K Resistor across the standby switch.

2. Fit a .05uF Capacitor from the hot side of the standby switch to ground.

3. Leave the standby switch on all the time like Reeltarded said.

I'm leaning towards the .05uF Cap on the hot side of the standby switch at the moment as I think this would help the situation and make the standby switch usable in case I lend my amp to someone who isn't in the know. I may also install diodes as protection for the valve rectifier but I just hate the idea of the valve rectifier blowing, the HT rising and biasing the power valves much hotter and me not noticing .

I know some people fit a .05uF Capacitor across the standby switch but I believe this only reduces arcing in the switch and nothing else.

[Littlewyan]

The amp is complete!

Started up first time without any issues so am chuffed with that. It sounds ok at the moment, may need some tweaking as I can't get a tone out of it that I really like and it doesn't seem to have enough gain. Going to do some valve swapping tomorrow as I know what these amps can do so I'm confident I can get my tone out of it .

One thing I am concerned about is I accidentally melted part of the 0.1uF Cap in the Phase Inverter circuit. Was holding my iron on a turret inbetween the 0.022uF Cap and 0.1uF Cap and slipped . I don't know if its affected the function of the cap or not, I did measure it and it measured 0.1uF so I think its ok.

Going to order a 0.05uF Capacitor to go on the hot side of the standby switch and may order a new 0.1uF Cap at the same time.

[norburybrook]

Very nice looks a lot neater than mine.

Mine does sound bloody amazing so I can put up with an ugly interior.

I ran mine for 6 months with all Suangueng Chinese valves then swapped the pre amp and PI valves for Watford valves;


ECC83/ECC83S/JJ-TESLA BALANCED (JJ Tesla) GBP 12.00 x 1 = GBP 12.00
ECC83-STR/HARMA (Harma) GBP 12.00 x 1 = GBP 12.00
ECC83-HARMA RETRO (Harma) GBP 16.00 x 1 = GBP 16.00


And noticed a nice improvement.



Marcus

[Reeltarded]

That is just beautiful! It's awesome!

Don't worry about the .1. I have a couple that I pin in for testing and they have more than a little heat rash.



Let's play it!!

[Littlewyan]

Thanks! Didn't expect that kind of response! I had a lot of fun building this amp. I will try and do a clip for you guys at some point, haven't got any proper recording equipment but I'll see what I can do!

I think the tone of the amp is off as I've got JJ ECC83S Valves in V2 and V3 which are very dull sounding compared to original Mullard 12AX7s! I've got a JJ ECC803S in V1 which can probably stay, tomorrow I'll try my EH12AX7s in the amp and my JJ ECC83MG. At the moment I'm having to run the bass on 0 and the rest of the controls on 10!

[Bob S]

Wow - that's nice. Definitely a keeper. Break in time.
Don't do what I do and get too previous with changes until you've got a few hours on her.
Nice one, well done.