1974 18w TMB with mods (cascade and PPIMV) - Tube Town Kit

[Warsaw]

Hope my experience culd be useful for those who want to approach to tube amp build. It's a great self - rewarding activity

After a lot of stompboxes and some amp repair, I've finally decided to graduate to tube amp building.

I've started from a Tube Town kit (TT kit Marshall style 18w TMB). They supply everything needed at very reasonable prices, with no import taxes for Europe (I'm in Italy).
Along with the kit I've taken also chassis, face and backplate, knobs, tolex, gold piping, rubber feet, handle.
Then I took also tolex, grillcloth, handles to build a SV212 replica, but this is another story.

I'm a Fender guy since now, but I was missing my '95 Sovtek MIG-100, that had the same circuit of a 2204, I used it a lot in the nineties when I used to play a lot live. I decided that I need a Marshall style amp.

For practice, gigging purpose and not least, weight and handling, at first I searched a Studio series second-hand, but both don't comply all the features that I need: mod friendly (no one), vintage look (SV20), versatilty (SC20), plexi flavour (maybe both).

So looking at the schematics I found the TMB 18w with some easy mods could be the live/practice tube head I was looking for.

This is my own interpretarions (mods) of the original Tube-town circuit:

1. Cascade mod (norm channel into TMB channel switchable with push pull potz)

2. Post phase inverter master volume (PPIMV type 2) - after tried the super-easy type 3 (works very well specially with linear potz) i've switched to type2 to see how it was, it's good and smooth regulation (double CST 1 meg lin potz in back plate)

3. Switchable Cathode bypass 0,68 uf cap in stage 2 of TMB (as tube-town suggest + 2,7k res) to get more gain with my strats (cap bypass) and to avoid muddy gain with my les paul (no cap bypass). Switch in backplate.

The head cabinet is made of poplar plywood taken at the local store, joint made simple with wood plugs and wood glue. The hardest part was doing radius and bevels, but since I love to work with electronics and wood, this project satisfied me a lot.

The result is outstanding, mostly tanks to the resources on Rob Robinette pages and forums (Marshallforum, TDPRI, 18watt and others).
It pairs perfectly with strats, tele of gibson guitars, with a hot and smooth tone, full of brillant frequencies, something close to a bluesbraker. With the TMB channel at full power recalls to me the early so-called plexi sound, and in cascade mode it goes in the jcm800 ballpark but can go further, without hissing, unwanted feedback.

To get the best out of it a good attenuator is suggested, so it's possible to run hot the power tubes. But also the post phase inverter master volume is useful if there isn't a power soak around.

I'm sorry for the logo applied but i consider a tribute to a great company.

 

[AndyD]

Excellent work!

 

[Steve2525]

Hope my experience culd be useful for those who want to approach to tube amp build. It's a great self - rewarding activity

After a lot of stompboxes and some amp repair, I've finally decided to graduate to tube amp building.

I've started from a Tube Town kit (TT kit Marshall style 18w TMB). They supply everything needed at very reasonable prices, with no import taxes for Europe (I'm in Italy).
Along with the kit I've taken also chassis, face and backplate, knobs, tolex, gold piping, rubber feet, handle.
Then I took also tolex, grillcloth, handles to build a SV212 replica, but this is another story.

I'm a Fender guy since now, but I was missing my '95 Sovtek MIG-100, that had the same circuit of a 2204, I used it a lot in the nineties when I used to play a lot live. I decided that I need a Marshall style amp.

For practice, gigging purpose and not least, weight and handling, at first I searched a Studio series second-hand, but both don't comply all the features that I need: mod friendly (no one), vintage look (SV20), versatilty (SC20), plexi flavour (maybe both).

So looking at the schematics I found the TMB 18w with some easy mods could be the live/practice tube head I was looking for.

This is my own interpretarions (mods) of the original Tube-town circuit:

1. Cascade mod (norm channel into TMB channel switchable with push pull potz)

2. Post phase inverter master volume (PPIMV type 2) - after tried the super-easy type 3 (works very well specially with linear potz) i've switched to type2 to see how it was, it's good and smooth regulation (double CST 1 meg lin potz in back plate)

3. Switchable Cathode bypass 0,68 uf cap in stage 2 of TMB (as tube-town suggest + 2,7k res) to get more gain with my strats (cap bypass) and to avoid muddy gain with my les paul (no cap bypass). Switch in backplate.

The head cabinet is made of poplar plywood taken at the local store, joint made simple with wood plugs and wood glue. The hardest part was doing radius and bevels, but since I love to work with electronics and wood, this project satisfied me a lot.

The result is outstanding, mostly tanks to the resources on Rob Robinette pages and forums (Marshallforum, TDPRI, 18watt and others).
It pairs perfectly with strats, tele of gibson guitars, with a hot and smooth tone, full of brillant frequencies, something close to a bluesbraker. With the TMB channel at full power recalls to me the early so-called plexi sound, and in cascade mode it goes in the jcm800 ballpark but can go further, without hissing, unwanted feedback.

To get the best out of it a good attenuator is suggested, so it's possible to run hot the power tubes. But also the post phase inverter master volume is useful if there isn't a power soak around.

I'm sorry for the logo applied but i consider a tribute to a great company.


View attachment 121650View attachment 121652View attachment 121653View attachment 121654View attachment 121655

Very nice Warsaw,

I am thinking of ordering this kit from Tube Town,

Are all the components in the last picture included with the kit or did you swap out components for higher quality items?

Is the power transformer an international version capable of 230 - 240 V

Did you have to order additional parts to mod it for the PPIMV

What schematic did you use to build the amp,

Regards,

Steve

 

[Central Scrutinizer]

Looks great!

 

[Marcomel79]

Beautiful work! Greetings from an Italian in Oslo!

 

[Warsaw]

Very nice Warsaw,

I am thinking of ordering this kit from Tube Town,

Are all the components in the last picture included with the kit or did you swap out components for higher quality items?

Is the power transformer an international version capable of 230 - 240 V

Did you have to order additional parts to mod it for the PPIMV

What schematic did you use to build the amp,

Regards,

Steve

1 - All the components are from the kit.

2 - The power transformer is 230-240v and could be tapped also for 120v - see image

3 - For the mods I bought a double gang pot for PPIMV and a push pull for cascade mode, and obviously some 0,5w resistors. I already have the switch for the cathode bypass cap (boost)

4 - I did the schematic, based on common and well experimented mods. Here you find also the layout.

 

[Steve2525]

Thanks for the info Warsaw,

I will order the extra parts for the PPIMV and Cascade mod too. Will research these mods while waiting for delivery of the kit from Tube Town.

What speaker do you use with this amp? I'm thinking a Celestion G12M 8 ohm???

And yes Rob Robinette's web site is excelent, using the info from Rob I have just finished building a 5E3 Tweed and have paired it with a A12Q speaker from tweeddeluxe.com

Regards,

Steve

 

[Steve2525]

Hi Warsaw,

I found the Trainwreck PDF on Rob Robinette's web site.

In your original post above:

Ref "2. Post phase inverter master volume (PPIMV type 2) - after tried the super-easy type 3 (works very well specially with linear potz) i've switched to type2 to see how it was, it's good and smooth regulation (double CST 1 meg lin potz in back plate)"

Was there a noticable difference between type 2 and type 3 PPIMV?

Also, Ref "1. Cascade mod (norm channel into TMB channel switchable with push pull potz)" what pot part number did you use for the cascade mod? DPDT Push Pull Volume 500KA ?

Regards,

Steve

 

[Warsaw]

Was there a noticable difference between type 2 and type 3 PPIMV?

Also, Ref "1. Cascade mod (norm channel into TMB channel switchable with push pull potz)" what pot part number did you use for the cascade mod? DPDT Push Pull Volume 500KA ?

PPIMV Type 3 is incredibly easy, but i found that it's not much linear, i've tried both with log and linear 1M pot but the results didn't satisfied me. The Type 2 gives a smoother volume raise, proportional to the pot rotation.
In addition, the type 2 act allow to control the power tube gain / saturation. It comes in need when you want a cleanish tone at high volume. With the PPIMV all open (stock amp condition), if you raise the master volume or the norm channel volume past about 6 the the amp begin to be overdriven.

If i want it to stay clean-ish, I just keep the PPIMV lower, then I control the ovedriven tone with pedals in a very classic boost configuraton (for e.g. a tube screamer with low gain high volume)

In the end, to appreciate at home all the flavours of this great amp I suggest to use an attenuator, but for convenience I use the PPIMV in practice room and live situations.

Think about it as a last adjustable gain stage. With the amp in cascade mode you have 4 controlled gain stages! You can try 2 stages preamp saturation, PI saturation and power tube saturation. It's a great platform to experiment many tones.


About the cascade mode: I ordered this: CTS Potentiometer 500k log, DPDT Standard Shaft p/n cpoA500k-pp
The same used for guitars. Very good pot and switch, but not very easy to wire and solder, surely could be much easier do this mod with a classic DPDT lever switch. But I wanted to keep as possibile the "classic" / vintage look of the amp, so I put in the back the boost switch, the PPIMV and used a push pull for cascade mode.

Thanks for the info Warsaw,

I will order the extra parts for the PPIMV and Cascade mod too. Will research these mods while waiting for delivery of the kit from Tube Town.

What speaker do you use with this amp? I'm thinking a Celestion G12M 8 ohm???

And yes Rob Robinette's web site is excelent, using the info from Rob I have just finished building a 5E3 Tweed and have paired it with a A12Q speaker from tweeddeluxe.com

Regards,

Steve

Research is a good thing for me to understand how it works and how I really want. In fact i have customized the cascade mode, because the schematics I found were inadequate to me.... causing a lot of blocking distortion. But just looking at a 2204 schematic I found the solution in grid stoppers....

At the moment I'm using a Celestion G12M 8ohm from a old fender M80 cab, but It's not too good to my ears.
In the reharsal room I use a 4x12 Randall cabinet... wow it's another planet! I'm currently building a 2x12 cab, will be loaded with a pair of fender 12" speakers from a '80 4x12 cab, will see how it goes.

Great resource the Rob Rob pages, It helped me a lot in restoring a silverface Vibrosonic.

 

[Warsaw]

Beautiful work! Greetings from an Italian in Oslo!

Thank you!

 

[Steve2525]

Thanks Warsaw,

Just placed my order with Tube Town, will report back when I start the build, may need to ask you more questions then,

I have not ordered a speaker yet. More research needed.

Regards,

Steve

 

[2L man]

Philipp has modified TT kit and to me it sound great. Obviously it has gone few mods and I found updated schematic perhaps in this YT comments. He did answer questions here about two years ago. I did ask which of the potentiometer holes have double potentiometers but I have lost it. I recall schematic has nine pots but faceplate has six knobs so three of them must be double pots?

 

[jagrenet]

Philipp has modified TT kit and to me it sound great. Obviously it has gone few mods and I found updated schematic perhaps in this YT comments. He did answer questions here about two years ago. I did ask which of the potentiometer holes have double potentiometers but I have lost it. I recall schematic has nine pots but faceplate has six knobs so three of them must be double pots?

I would be curious to know the specs of this mod. Sounds really good.

 

[2L man]

I would be curious to know the specs of this mod. Sounds really good.

There is a link to the schematic on that YT. That new has changes to what Philipp discussed here about two-three years ago. Like I already wrote that amp faceplate has six pot knobs but schematic has nine pots so obviously three are dual pots. Knobs looks like none is staggered pots. So I think it is essential to know which functions are paired?

 

[jagrenet]

There is a link to the schematic on that YT. That new has changes to what Philipp discussed here about two-three years ago. Like I already wrote that amp faceplate has six pot knobs but schematic has nine pots so obviously three are dual pots. Knobs looks like none is staggered pots. So I think it is essential to know which functions are paired?

Thank you. Originally, I just watched the clip on this forum rather than YT. I just looked at the schematic and found a couple of interesting changes in the preamp that I plan to implement, just as a test. Namely, removing the 22nf and the 4k7 coupling caps and replacing them with the 3.3nf, on the way into V2A. The rest of the "extra" pots can come later. Ffirst I want to see what the above mentioned change will provide. Thanks again !!

 

[Warsaw]

Just an update, the cab is completed... way more easier build an amp to me.



And soon the channel switching will be modified with a pair or relays, to let me use a footswitch.