Need help with new build idea for two amps in one

[Mike_J]

Does anyone think I could make an amp with two entire amps in it?  I am currently building a Sluckey inspired Plexi/800 amp and am waiting on the power transformer to arrive.  What I was think of is a JTM 45 with either a Plexi or 800.  Each preamp would have their own volume controls, tone stack and PI.  The JTM 45 would have either two 5881s or KT 66s and the Plexi or 800 would have two EL34s.  This would make for two 50 watt amps in one cabinet.  Both amps would have separate PPIMVs.

The power transformer I am thinking about using is one I have on hand.  It has a 173-145-0-145-173 volt at 450 mA HT secondary.  Should make about 410 or 490 volts of B+ depending on the tap I select.  I would think the 410 tap would be best if I choose 5881s for the JTM45 side.  May be able to go with the higher voltage if I use KT66s.

Not sure what output transformer or choke to use.  Should probably be 100 watts in case I want to play both channels at the same time.

Does anyone have any input they could provide?

Thanks
Mike

[tubenit]

Either Physconoodler or Loose Change built two amps into one chassis once. I think one was a Marshall amp.

They were side by side in a long chassis and NOT double stacked from what I remember? 

Anyone remember who it was that actually did that?  I think they said it was successful but had a little more noise/hum then they had hoped?  It was maybe 5-7 yrs ago?

My impression was the chassis was huge and would be OK set in place but impractical and cumbersome to move around at all.

With respect, Tubenit

[Mike_J]

Either Physconoodler or Loose Change built two amps into one chassis once. I think one was a Marshall amp.

They were side by side in a long chassis and NOT double stacked from what I remember? 

Anyone remember who it was that actually did that?  I think they said it was successful but had a little more noise/hum then they had hoped?  It was maybe 5-7 yrs ago?

My impression was the chassis was huge and would be OK set in place but impractical and cumbersome to move around at all.

With respect, Tubenit

Tubenit

Thank you for the reply.  I am not sure why the chassis would have to be so large.  It would require four power tubes and six preamp tubes.  An AB763 has at least as many tubes.  I am not thinking about having two sets of transformers. 

With a 100 watt PT I would think I could run two sets of two tubes.  One of the preamps would use two of the push-pull tubes and the other preamp would use the other two tubes.  I was thinking the biggest problem would be with the OT as a 5881 50 watt amp is 8K while the EL34 amp is I believe in the 3.3K range.  I am just guessing this would work but don't see why it would not but I could very well be wrong.

I read somewhere early on Marshall used two 50 watt transformers for their early 100 watt amps because of availability of parts at the time.  I am pretty sure they were power transformers but if they were output transformers then that would be my solution.  I could run two 50 watt output transformers at 8 ohms each into my 212 cabinet with Creamback 12M65s in stereo mode.

Thanks
Mike

[John]

But won't you also need room for 2 circuit boards?

[Mike_J]

But won't you also need room for 2 circuit boards?

John

Thank you for your reply.  I can use one circuit board.  The board for my Sluckey inspired Plexi/800 is somewhere in the neighborhood of 17 inches long.  It includes the volume controls and tone stacks for both amps but shares a common PI.  It also has an active fx loop and an overdrive channel so it is more involved than the amp I am proposing here.  All I would be adding is room for one more PI section and eliminating the fx and overdrive sections.  I would also run the bias boards on the face of the amp to save space.  See attached picture on how I did it for the Sluckey inspired amp.

The bias board is next to the PPIMV 250K dual pot which makes the wire runs shorter.  I would need two with two PI sections and two sets of tubes.

Thanks
Mike

[tubenit]

Mike,

I simply didn't understand what you were considering doing. IF I am understanding it now, then I think your idea may work.

With respect, Tubenit

[Mike_J]

Mike,

I simply didn't understand what you were considering doing. IF I am understanding it now, then I think your idea may work.

With respect, Tubenit

Thanks Tubenit

I read an article by Ken Fischer in one of Weber's books and it said that Marshall was having trouble getting 100 watt OTs so they used two 50 watt OTs for their first 100 watt amps.  Therefore, I don't see why I couldn't do the same.  Have one OT for the two EL34s and another for the 5881s or KT66s.  Do you think that would work?

Thanks
Mike

[Mike_J]

Just thought of a problem.  The JTM45 used a GZ34.  I need a full wave rectifier for the voltage doubler for the PT I have.  Also need solid state rectification for the Plexi/800 side.  Can anyone think of a solution to this problem?

Thanks
Mike

[kagliostro]

As I haven't exactly understand your intentions I don't know if this kind of doubler can help you


(look to the right doubler that uses a double diode rectifier)





Give a look also here

http://www.bunkerofdoom.com/lit/4x8/






K

[Mike_J]

As I haven't exactly understand your intentions I don't know if this kind of doubler can help you


(look to the right doubler that uses a double diode rectifier)





Give a look also here

http://www.bunkerofdoom.com/lit/4x8/






K

Thanks Kagliostro

What I want the JTM45 to provide is a cleaner signal than the Plexi or 800 channel.  Will probably use the higher tap on the PT in order to increase headroom on the 45 which will require the use of KT66s.  Using the normal Plexi voltage doubler solid state rectification should also result in more headroom for the clean (JTM45) channel and would be consistent with Plexi or 800 specs.

When I get more time I will put a schematic together showing what I am talking about.  It will essentially have these features:

JTM45 Normal Volume and Bright Volume - Tone stack - PI - PPIMV - 8K ohm 50 watt OT - Middle two tubes (KT66s) fed by 100 watt PT.

Plexi or 800 Normal and Bright or Master Volume - Tone stack - PI - PPIMV - 3.3K ohm 50 watt OT - Outside two tubes (EL34s) fed by the 100 watt PT.

Hope this makes sense.  Basically, my goal is to make use of the 100 watt PT I have and end up with two 50 watt amps that can be somewhat attenuated by their PPIMVs.  I will already have a Plexi/800 amp so this amp would just be a little different.

Thanks
MIke

 

[Ed_Chambley]

It was Psyconoodler that built a Marshall 18 and Princeton in the same combo cab.  There is a photo on the website of it.  He used 2 separate chassis.

A lot of the old organ tone cabinets were sort of like this.  They had 2 Output Transformers, one for the bass and another for treble which also had an oil tank reverb.  Very similar except they need a preamp.

Have a look at the Hammond JR20 Tone cabinet schematic.  I have a marshall 50/50 amp.  It has no preamp, just an amp.  I can run one side with kt66 and the other with EL34 and plug a preamp into either side.  A stereo amp.

[Mike_J]

It was Psyconoodler that built a Marshall 18 and Princeton in the same combo cab.  There is a photo on the website of it.  He used 2 separate chassis.

A lot of the old organ tone cabinets were sort of like this.  They had 2 Output Transformers, one for the bass and another for treble which also had an oil tank reverb.  Very similar except they need a preamp.

Have a look at the Hammond JR20 Tone cabinet schematic.  I have a marshall 50/50 amp.  It has no preamp, just an amp.  I can run one side with kt66 and the other with EL34 and plug a preamp into either side.  A stereo amp.

Ed

Thank you for the reply.  I will look at the Hammond JR20 Tone cabinet schematic.  I already have a 25-1/2" X 8-1/2" X 3" chassis that should be large enough for this project.  I will use 16mm pots for controls so I can stack them, the only way I can see to get the two amps in one chassis. 

I am not familiar with the Marshall 50/50 amp.  Is it an amp you made or an actual Marshall product?

Thanks
Mike

[kagliostro]

I think that also only a block schematic will be of great help in order to understand exactly what you want to do


K

[Mike_J]

I think that also only a block schematic will be of great help in order to understand exactly what you want to do


K

I have attached schematics of the JTM45/800 amp.  My apologies for the hen scratch.  I have yet to master any of the schematic software.

Not sure about the two bias supplies the way I have them drawn.

Thanks
Mike

[kagliostro]

So you want to build a pair of complete amps in the same cabinet with one PT and one (100W) OT 

You have a PT with secondary at 173-145-0-145-173 volt @ 450 mA
(is the 450mA AC rated ?  --   there is a 6.3v or 12.6v winding for heaters, which current ?)

and a single 100W OT to which you want to connect a pair of tubes that are part of the 800 circuit and a pair that are part of the JTM45 circuit

As far I can know, the power tube can be different, but their request in impedance must be very similar

Also, if you use a single OT you can't use different voltage for each circuit Power Section, the only thing you can do is to have different voltages at the preamp circuit, not to the power tubes

Or I've misunderstand you and you want to build two circuits supplied with a single PT feeding two (50W) OT (one for each circuit) like in HiFi Stereo Amps ?

K

[terminalgs]

There were a few guitar amps in the 60's that did this (sorta).  You can easily find the schematics if you want to see how they laid out the power supplies:  The Ampeg Echo-Twin used  two PTs and two OTs,  the Gibson GA79RVT and the Magnatone M15 both used a single PT and two OTs.   There are also a bunch of valco 70W that used two 35W OTs,  but they all shared PI's.  Nonetheless, they might give you ideas too: S6699, 62-9052A to name two..


The GA79RVT instrument signals never cross or get mixed inside the two amplifiers, but there is a stereo inst. jack in front of the two preamps that let use a single input to drive both amps.  The M15 has that as well, but it also mixes Ch.1 & Ch.2 preamp outs to send to one output section, and it does the same for the other.  It also has dual vibrato units that run off the same oscillation section either in-sync, or 180* out,  it sends one vib to one output and one to the other.


I'm sure at minimum, you'll want the option to drive both amps with a single instrument singal.  Those amps will give you ideas on how to wire the input jacks.  There are also ideas to mix the signals post preamps (optional with switches).

[Ed_Chambley]

It was Psyconoodler that built a Marshall 18 and Princeton in the same combo cab.  There is a photo on the website of it.  He used 2 separate chassis.

A lot of the old organ tone cabinets were sort of like this.  They had 2 Output Transformers, one for the bass and another for treble which also had an oil tank reverb.  Very similar except they need a preamp.

Have a look at the Hammond JR20 Tone cabinet schematic.  I have a marshall 50/50 amp.  It has no preamp, just an amp.  I can run one side with kt66 and the other with EL34 and plug a preamp into either side.  A stereo amp.

It is am actual Marshall product.  They still make it but it is called something else.  It is a lot of fun having both tube types together.  Used they are a great deal, but they are heavy.  They also make a 100/100.

http://www.marshallamps.com/products/amplifiers/rack-power-amps/

I bought mine cheaper than half the iron cost.

Ed

Thank you for the reply.  I will look at the Hammond JR20 Tone cabinet schematic.  I already have a 25-1/2" X 8-1/2" X 3" chassis that should be large enough for this project.  I will use 16mm pots for controls so I can stack them, the only way I can see to get the two amps in one chassis. 

I am not familiar with the Marshall 50/50 amp.  Is it an amp you made or an actual Marshall product?

Thanks
Mike

[Mike_J]

So you want to build a pair of complete amps in the same cabinet with one PT and one (100W) OT 

You have a PT with secondary at 173-145-0-145-173 volt @ 450 mA
(is the 450mA AC rated ?  --   there is a 6.3v or 12.6v winding for heaters, which current ?)

and a single 100W OT to which you want to connect a pair of tubes that are part of the 800 circuit and a pair that are part of the JTM45 circuit

As far I can know, the power tube can be different, but their request in impedance must be very similar

Also, if you use a single OT you can't use different voltage for each circuit Power Section, the only thing you can do is to have different voltages at the preamp circuit, not to the power tubes

Or I've misunderstand you and you want to build two circuits supplied with a single PT feeding two (50W) OT (one for each circuit) like in HiFi Stereo Amps ?

K

You are correct about misunderstanding what I am trying to do.  I want to in fact use one 100 watt PT and two 50 watt OTs.  The two OTs will have separate speaker jacks and will be fed in stereo to my 212 cabinet with Celestion 12M65 Creambacks.

Thanks
Mike

[Mike_J]

There were a few guitar amps in the 60's that did this (sorta).  You can easily find the schematics if you want to see how they laid out the power supplies:  The Ampeg Echo-Twin used  two PTs and two OTs,  the Gibson GA79RVT and the Magnatone M15 both used a single PT and two OTs.   There are also a bunch of valco 70W that used two 35W OTs,  but they all shared PI's.  Nonetheless, they might give you ideas too: S6699, 62-9052A to name two..


The GA79RVT instrument signals never cross or get mixed inside the two amplifiers, but there is a stereo inst. jack in front of the two preamps that let use a single input to drive both amps.  The M15 has that as well, but it also mixes Ch.1 & Ch.2 preamp outs to send to one output section, and it does the same for the other.  It also has dual vibrato units that run off the same oscillation section either in-sync, or 180* out,  it sends one vib to one output and one to the other.


I'm sure at minimum, you'll want the option to drive both amps with a single instrument singal.  Those amps will give you ideas on how to wire the input jacks.  There are also ideas to mix the signals post preamps (optional with switches).

Thanks for the excellent information Terminalgs.  I was thinking of having separate inputs for each channel and using an external A/B/Y box to process the signal to the inputs.  I will look at the amps that you have suggested to see what they did.

Thanks
Mike

[Mike_J]

It was Psyconoodler that built a Marshall 18 and Princeton in the same combo cab.  There is a photo on the website of it.  He used 2 separate chassis.

A lot of the old organ tone cabinets were sort of like this.  They had 2 Output Transformers, one for the bass and another for treble which also had an oil tank reverb.  Very similar except they need a preamp.

Have a look at the Hammond JR20 Tone cabinet schematic.  I have a marshall 50/50 amp.  It has no preamp, just an amp.  I can run one side with kt66 and the other with EL34 and plug a preamp into either side.  A stereo amp.

It is am actual Marshall product.  They still make it but it is called something else.  It is a lot of fun having both tube types together.  Used they are a great deal, but they are heavy.  They also make a 100/100.

http://www.marshallamps.com/products/amplifiers/rack-power-amps/

I bought mine cheaper than half the iron cost.

Ed

Thank you for the reply.  I will look at the Hammond JR20 Tone cabinet schematic.  I already have a 25-1/2" X 8-1/2" X 3" chassis that should be large enough for this project.  I will use 16mm pots for controls so I can stack them, the only way I can see to get the two amps in one chassis. 

I am not familiar with the Marshall 50/50 amp.  Is it an amp you made or an actual Marshall product?

Thanks
Mike

Thanks Ed

I am going to keep my eye open for a 50/50 model because that is the wattage range I am interested in.  I still like the idea of having separate PPIMVs on each preamp to further reduce volume somewhat.  I have been building a lot of 100 watt amps lately which can be played at reasonable volumes.  It seems however sensible to have the two 50 watt OT variant to match up with the 100 watt PT I already have.  Using the JTM45 with a 100 watt PT should provide ample headroom on the clean channel and having the normal master volume and the addition of the PPIMV will hopefully still allow for plenty of Marshall crunch on the overdrive (800) channel.

Thanks
Mike

[sluckey]

Have you abandoned your other dual project?

[Mike_J]

Have you abandoned your other dual project?

Hi Sluckey

No I haven't abandoned my other dual project.  I ordered a new PT because my other PT was 100 mA short of heater current capacity.  Probably not a problem but I want the amp to last so I had them increase the heater current from 8 amps to 9.3 amps.  Shouldn't be a problem then.  That is why I have the extra 100 watt PT for this build.  The idea for the build I am discussing in this post is just another extension of the Sluckey inspired Plexi/800 amp.

The new PT is supposed to be shipped this coming Thursday so I should get it next week.  I will have everything wired except for the PT by the time it comes in. 

I will try to get my photographer to take current pictures of my build when she gets home from school tomorrow.

Thanks
Mike

[kagliostro]

So you want to build a guitar amp with the same architecture of an HiFi Stereo amp (one PT and two OT)

I think that a separated PPIMV will be a good idea and also to join the two channel within the amp seems a good one

I'm not sure you can join the two amp at the input of the two PI like in the Gibson GA79RVT

but you can join the two input of the amp with a switch or using a dedicated input jack

About the PS you can arrange two distinct complete circuits connected to the same PT as to have on each PS the voltages you need for each amp

EDIT: I was looking for jtm45 and jcm800 PT spec, I've find info about jcm800 PT having 350v or 360v, but about jtm45 I've find indication about PT with 345v and other saying 300v

Which are the correct voltages for the PT of this two amps ??

K

[Mike_J]

So you want to build a guitar amp with the same architecture of an HiFi Stereo amp (one PT and two OT)

I think that a separated PPIMV will be a good idea and also to join the two channel within the amp seems a good one

I'm not sure you can join the two amp at the input of the two PI like in the Gibson GA79RVT

but you can join the two input of the amp with a switch or using a dedicated input jack

About the PS you can arrange two distinct complete circuits connected to the same PT as to have on each PS the voltages you need for each amp

EDIT: I was looking for jtm45 and jcm800 PT spec, I've find info about jcm800 PT having 350v or 360v, but about jtm45 I've find indication about PT with 345v and other saying 300v

Which are the correct voltages for the PT of this two amps ??

K

Kagliostro

Thank you for the reply.  My guess is 300 volts would be appropriate for the original 5881 tubes in the JTM45.  When they changed to KT66s and dropped the GZ34 in favor of solid state rectification they increased the voltage into the 345 to 360 volt range.  My PT HT is 346 volts which is in the range for KT66s and EL34s.

You are correct about the stereo amp, one PT and two OT concept.  Want to be able to play them separately or together.  Will need separate output sections to accomplish that however as I believe the amps might not be in phase with each other.  With separate output sections I could switch poles on the output jacks and get them in phase.

The PIs are where I am most concerned but I haven't had time to give it much thought as I am working on another amp at this time.  Will look at the Gibson amp for ideas though. 

Agree with you about splitting the voltage in the power supply.  I had to split them a few times on the Sluckey inspired Plexi/800 with OD & FX amp I am working on now.  It has two tone stacks but shares a PI so I have not had to tackle the PI issue.  My guess is Sluckey will know exactly what I need to do when the time comes to solve the dual PI question.

Thanks
Mike

[kagliostro]

My guess is 300 volts would be appropriate for the original 5881 tubes in the JTM45.  When they changed to KT66s and dropped the GZ34 in favor of solid state rectification they increased the voltage into the 345 to 360 volt range.  My PT HT is 346 volts which is in the range for KT66s and EL34s.

I think that your 175-145-0-145-175 PT with SS rectify will be fine also for 5881 + EL34 (or KT66) tubes



K

[Mike_J]

My guess is 300 volts would be appropriate for the original 5881 tubes in the JTM45.  When they changed to KT66s and dropped the GZ34 in favor of solid state rectification they increased the voltage into the 345 to 360 volt range.  My PT HT is 346 volts which is in the range for KT66s and EL34s.

I think that your 175-145-0-145-175 PT with SS rectify will be fine also for 5881 + EL34 (or KT66) tubes



K

Kagliostro

Thank you for the drawing. 

I was leaning towards the KT66s because I think they might give me a little more headroom and I would use the JTM45 side as my clean channel although I know with pedals it could be much more than a clean channel.  However, I have always liked the sound of the 5881s and the reissue Tung Sols are pretty decent power tubes.

I think it might be prudent to make the amp with two full wave rectifiers as you have drawn it so that either option could be utilized.  Thank you for the suggestion.

Thanks
Mike