Two different preamps (one octal and one regular) in a Tweed Delux "clone"

[Wyatt]

I see this project as a bit of a non-starter, ...

• The chassis would have to be custom bent and punched, there is no doing this with an existing Tweed style chassis. There isn't a chassis out there with enough octal preamp holes. You could probably rework something like a Super reverb chassis
• The power transformer has a lot supply a lot of heater current and still have the proper high tension voltage
  
• It would need a custom power sting, with a lot of nodes, because the Gibson amps ran on about 100 volts less B+ with a poor current supply
• Octal preamp tubes are finicky, they have their tone benefits are are hard to keep quiet. The tone of the Gibson amp isn't in the octal tubes, but the overall tone stack and design, the noval GA-20 still sounded like a GA-20
• As noted, the tubes listed include two channels and a PI for each circuit, it's going to have to be a compromise of either or, especially on PI

It's the kind of fun, dream-amp project a kid gets to doodle in their notebook with no limitations (it's certainly right up my alley taste-wise). But the idea needs to be streamlined for reality and Gibson already did that with the GA-40 Les Paul. It gives the classic Gibson jazz tone and swampy tremolo and can sound close enough to a Tweed Deluxe for rock 'n' roll, or could have one channel re-voiced for more top end and gain.

 

[printer2]

Something to think about. Fender used the Paraphase phase inverter in earlier Deluxes. Just need a volume for the 6SJ7, the Deluxe tone control will act on it. The volume for the pentode can be a push-pull switch to give the versatility of a cathode bias (cleaner) along with grid leak bias. Or just leave it grid leak. Going all the way and using 6SC7's would be interesting. Think with a little work it can fit in a Tweed Vibrolux-Style-5F11 chassis.

I think you might have talked me into another amp.

 

[Jesco]

you need to try and enlist the help of RobRob

I would also add here that I don’t necessarily think we should direct people to seek the help of Rob. He has given an extraordinary amount of his time to the amp building community, and I think we should let Rob decide when and where he wants to jump in on a project. There are a lot of brilliant minds on this forum, and the beauty is that those folks can jump on a project when whim and time unite.

 

[Jerry garrcia]

I see this project as a bit of a non-starter, ...

• The chassis would have to be custom bent and punched, there is no doing this with an existing Tweed style chassis. There isn't a chassis out there with enough octal preamp holes. You could probably rework something like a Super reverb chassis
• The power transformer has a lot supply a lot of heater current and still have the proper high tension voltage
  
• It would need a custom power sting, with a lot of nodes, because the Gibson amps ran on about 100 volts less B+ with a poor current supply
• Octal preamp tubes are finicky, they have their tone benefits are are hard to keep quiet. The tone of the Gibson amp isn't in the octal tubes, but the overall tone stack and design, the noval GA-20 still sounded like a GA-20
• As noted, the tubes listed include two channels and a PI for each circuit, it's going to have to be a compromise of either or, especially on PI

It's the kind of fun, dream-amp project a kid gets to doodle in their notebook with no limitations (it's certainly right up my alley taste-wise). But the idea needs to be streamlined for reality and Gibson already did that with the GA-40 Les Paul. It gives the classic Gibson jazz tone and swampy tremolo and can sound close enough to a Tweed Deluxe for rock 'n' roll, or could have one channel re-voiced for more top end and gain.

That's what this is, a fun, dream-amp project. My original question in this thread was if it is possible to make such an amp with the "2 in 1" configuration/sound in a single combo style cabinet? I don't have enough knowledge regarding this matter so I asked the question in this forum, where people with more knowledge than me picks their brains, if it could be done? If it is impossible, like the question if a particle with mass could travel at the speed of light, I'm letting it go. If not (due to laws of physics or that there are no transformers to buy that can handle it etc), I will proceed with the quest to build the dream-amp. I could probably buy a GA-20/40/50 in good condition, or a Sequel Tribute, or a Vintage 47 or a Octal Delux AND a Tweed Deluxe but that's not as fun as building one amp that has the possibility to combine the sounds in one amp. If anybody could help me with the answer to the question if it is possible I would be delighted. If anybody also has an idea on how it could be done I would be even more delighted. Happy Friday/weekend!

 

[printer2]

As well as my eyes can see the values on the schematic. Added grid stoppers and 1 ohm resistors.

 

[Tele Slacker]

Is this similar to what you’re looking for (from Angela Instruments catalog)?

 

[printer2]

Part of the sound is the Paraphase inverter. It adds some fatness to the sound if a little unbalanced. That and the grid leak bias on the pentode in front (where the cathode is grounded). I think it sounds better for cleaner stuff with a touch of hair than the cathodyne in the 5E3. The 10k as compared to the 5k in the power supply to the screens also gives it a softer sound.

The Angela rout is not bad either but I do not like the idea of pulling and reinserting tubes as a way to switch things. More practicle,

Stick it in a 5E3 chassis. Use solid state diodes and a sag resistor instead of the tube rectifier. Move the 6V6's over one hole. You use the freed up octal hole for the 6SJ7, either use the standby switch position for the double pole switch or you can get a push-pull switch on the volume control.

 

[Jerry garrcia]

Part of the sound is the Paraphase inverter. It adds some fatness to the sound if a little unbalanced. That and the grid leak bias on the pentode in front (where the cathode is grounded). I think it sounds better for cleaner stuff with a touch of hair than the cathodyne in the 5E3. The 10k as compared to the 5k in the power supply to the screens also gives it a softer sound.

The Angela rout is not bad either but I do not like the idea of pulling and reinserting tubes as a way to switch things. More practicle,

Stick it in a 5E3 chassis. Use solid state diodes and a sag resistor instead of the tube rectifier. Move the 6V6's over one hole. You use the freed up octal hole for the 6SJ7, either use the standby switch position for the double pole switch or you can get a push-pull switch on the volume control.

Thank you for your help! I have talked to a amp builder and vendor of components and he agrees with you. I will now consult him for help with constructing a building schematics and a mounting board. It it is a leap of faith but it is only money and time right I am really looking forward to this built in this ocean of Covid-19 diarrhoea.
Once again, thanks.

 

[printer2]

Thank you for your help! I have talked to a amp builder and vendor of components and he agrees with you. I will now consult him for help with constructing a building schematics and a mounting board. It it is a leap of faith but it is only money and time right I am really looking forward to this built in this ocean of Covid-19 diarrhoea.
Once again, thanks.

Well it is nice when my effort helps someone. (What! you showed this to someone else!!!) Good luck. I do think it should turn out alright.

 

[Jerry garrcia]

Well it is nice when my effort helps someone. (What! you showed this to someone else!!!) Good luck. I do think it should turn out alright.

Me too. As I wrote before I’m a newbie at these things but learning as I move forward. I think I have a beginning of a building schematic but can’t get a grip at the power supply part. Like with the power transformer part in the build schematics. Is it too much to ask for a little help with that? I have realised that your idea is as close to the construction I’m looking for since it was a naive idea to think that I could get a double preamp in a single combo tweed deluxe cabinet.

 

[printer2]

It is always tough to get ten pounds in a five pound sack. Just a question of tradeoffs then. If you really want it the way to do it is use a bigger chassis and cut the cabinet panel area wider. Say a Tweed Super/Pro. (Not that I checked if it would fit in a 5E3). That gives you more room to accommodate stuff. Maybe use a four pole rotary switch to connect the input jacks and the output grids. Probably should not mention it at this time.

 

[Jerry garrcia]

It is always tough to get ten pounds in a five pound sack. Just a question of tradeoffs then. If you really want it the way to do it is use a bigger chassis and cut the cabinet panel area wider. Say a Tweed Super/Pro. (Not that I checked if it would fit in a 5E3). That gives you more room to accommodate stuff. Maybe use a four pole rotary switch to connect the input jacks and the output grids. Probably should not mention it at this time.

I will probably see what kind of chassi and cabinet needed once I’m done with the building schematic. The component part soon done.
Is it to much to ask for some help with the power supply schematic? I can’t get a grip of that one.

 

[printer2]

I will probably see what kind of chassi and cabinet needed once I’m done with the building schematic. The component part soon done.
Is it to much to ask for some help with the power supply schematic? I can’t get a grip of that one.

It depends on what you are having for a power transformer, what voltages you get. Download Duncan's calculator and play around a little.

http://www.duncanamps.com/psud2/download.html

 

[Jerry garrcia]

It depends on what you are having for a power transformer, what voltages you get. Download Duncan's calculator and play around a little.

http://www.duncanamps.com/psud2/download.html

Once again, thank you! Will now move forward.

 

[Jerry garrcia]

I finally got hold of a 6SC7 tube so the build is starting. All components ordered and had som problem with the power supply schematics but hopefully a builder I a town close by will be helping me with that. Speaker will be a Jensen P12N for a clear sound that hopefully will balance the octal tube part. Soon we’ll hear how it sounds with an archtop with CC pickups.
Cabinet will resemble of a Sequel Tribute since it is close to a Gibson GA-50 with just one speaker. mot might be a nice Christmas present if it works out as I want.

 

[The Ballzz]

There's likely enough extra real estate in the cabinet to accommodate the extra size of a chassis to accomplish this "two separate preamp" build. The cutout in the top of the cabinet may need to be a little wider to possibly allow for an extra pair of jacks, switches or other! And as mentioned earlier the magic of the Tweed Deluxe (multiple versions) is the channel interaction, whether channel jumpered or not. And then we're at the point of needing to think about the added current draw on both the B+ rail and heaters. A stock 5E3 transformer is already well taxed in standard form! Cool idea though.
Just My $.02,
Gene

 

[Jerry garrcia]

It depends on what you are having for a power transformer, what voltages you get. Download Duncan's calculator and play around a little.

http://www.duncanamps.com/psud2/download.html

Hi and hope you are doing well. Do you have any inputs on this?

 

[andrewRneumann]

View attachment 930010
Hi and hope you are doing well. Do you have any inputs on this?

I am doing great. You? I will start with this: the valve pin numbering is reversed. The numbers start the key/gap and increase going clockwise.

It appears you are using a bridge rectifier when a simple full wave rectifier using only 2 diodes is required.

I have multiple other questions/concerns. I think they would be easier to point out and understand on schematic. Can you post the schematic that goes along with this layout? More to come…

Proper rotation for the gang:

 

[andrewRneumann]

I humbly offer this for the PI—>Power Tube circuit. The 47k leg of the voltage divider could initially be a 50k linear pot for test purposes.

 

[andrewRneumann]

Here’s an idea for the power supply without changing the location of anything.

If I were designing this, I would probably add another supply capacitor and dropping resistor (or two). Not sure it would be required in your case, but I always play it safe and decouple pairs of valves. Looks like you have 6 valves running off of C11, which seems like a lot and might lead to some interesting low frequency oscillations.