Considerations for an 18 watt Liverpool?

[ViperDoc]

I’m really tempted by the Liverpool, d*mn you, Pete Thorn!!!!

I want to build a full power version, but how would a Liverpool preamp into a 18 watt British power section work with Radiospares-spec transformers? KF’s filtering arrangement is unique. How would you alter the circuit if at all? This has to have been done already.

[pompeiisneaks]

I’m really tempted by the Liverpool, d*mn you, Pete Thorn!!!!

I want to build a full power version, but how would a Liverpool preamp into a 18 watt British power section work with Radiospares-spec transformers? KF’s filtering arrangement is unique. How would you alter the circuit if at all? This has to have been done already.

One of the general tone constructs of the liverpool imo is the EL84 output tubes... pushing it into some 6v6's is going to change that I'd think... If you want lower wattage you could go to 2 power tubes instead of 4, but up to you.

~Phil

[Mac Dillard]

The 18 watt Marshall is 2 EL84 p/p with EZ81 tube rectifier

[ViperDoc]

I was thinking 2xEL84 with a SS rectifier. Curious about the power supply, whether the filtering would stay the same in the output section.

LIKE THIS: JUST A DRAFT, NOT TESTED!

VIPERDOC 18W LIVERPOOL-DRAFT.pdf

[pompeiisneaks]

The 18 watt Marshall is 2 EL84 p/p with EZ81 tube rectifier

oh woops hehe, guess I blew that I've never built one, made a bad assumption.

~Phil

[Mac Dillard]

Not so far off, most of the 18 watt PT that I have looked at are 290-0-290. With the EZ81 that puts you at a rectified voltage of about 350 vdc for the EL84 plates and they drop the screen voltage down some from that...That PT with the SS rectifier will probably give you about 410 vdc...Don't think the EL84s will like that much voltage. That puts you at the voltage a 6V6 would operate at. But, I am over my head here. I just build them. Don't design them. Even with the tube rectifier the screen B+ node dropping resistor will have to be increased...Maybe up to around 2K,

[ViperDoc]

That preamp schematic and notes are copied from the Liverpool SCH in the TW Documents thread here for consistency. I left the voltages on this SCH that are listed on that original drawing. I would assume you'd want to keep those the same. To your point, the B+ would need to be dropped appropriately to hit the proper A node voltage.

[Colossal]

Hi ViperDoc,

Not trying to talk you out of it or anything, but any reason you are considering a 2xEL84 versus the full power version? Transformers on hand? Just because? The Liverpool, like the Express is a handful. Great, great amps that do their magical thing.

[ViperDoc]

I'm going to build the full version for sure. However, these days I'm barely able to turn my 5E3 past "2" on the gain knobs before people ask me to turn down at gigs. We are suffering for real tone, brethren! It may be a fool's errand, but I wondered it the KF magic could be squeezed out of a lower output platform. As far as 18-watt transformers, I have a few GDS (Heyboer) 18-watt PT/OT pairs for 18-watt Marshalls and some Classictone 20-watt Deluxe Reverb PT/OT pairs for DR builds.

In this SCH doc off of EL34world.com, Mark Abbott makes a screen resistor value recommendation for an 18-watt build, but with no other recommendations.

Trainwreck_liverpool.pdf

[Colossal]

I'm going to build the full version for sure. However, these days I'm barely able to turn my 5E3 past "2" on the gain knobs before people ask me to turn down at gigs. We are suffering for real tone, brethren! It may be a fool's errand, but I wondered it the KF magic could be squeezed out of a lower output platform. As far as 18-watt transformers, I have a few GDS (Heyboer) 18-watt PT/OT pairs for 18-watt Marshalls and some Classictone 20-watt Deluxe Reverb PT/OT pairs for DR builds.

In this SCH doc off of EL34world.com, Mark Abbott makes a screen resistor value recommendation for an 18-watt build, but with no other recommendations.

Trainwreck_liverpool.pdf

Ah, yes, everyone's problem now....volume You can get the amp to do what it is supposed to in a 2xEL84 format, however, it won't be at any significant reduction in volume. It will be as loud or louder than an 18W cascaded amp. A less efficient speaker like a Greenback can certainly help along with an attenuator to knock off a few more dB. One of the key features of the Trainwreck response is the increased primary impedance. The Liverpool runs at 6k6 for a quad of EL84s, as opposed to the usual 4k you see with AC30s (whose load lines are cast right out of the RCA Handbook). This will increase power amp distortion and increase screen current for large voltage swings. You will want to stick with the stock 1k screen resistors and increase the screen dropping resistor in the power supply from 1k to 2k2 (like an 18W) to get the screen supply down to about 317VDC.

[ViperDoc]

Ah, yes, everyone's problem now....volume You can get the amp to do what it is supposed to in a 2xEL84 format, however, it won't be at any significant reduction in volume. It will be as loud or louder than an 18W cascaded amp. A less efficient speaker like a Greenback can certainly help along with an attenuator to knock off a few more dB. One of the key features of the Trainwreck response is the increased primary impedance. The Liverpool runs at 6k6 for a quad of EL84s, as opposed to the usual 4k you see with AC30s (whose load lines are cast right out of the RCA Handbook). This will increase power amp distortion and increase screen current for large voltage swings. You will want to stick with the stock 1k screen resistors and increase the screen dropping resistor in the power supply from 1k to 2k2 (like an 18W) to get the screen supply down to about 317VDC.

Very good. What about the filter caps, such as the 80 uF vs. the 32 uF in the 18 watt Classic?

[Colossal]

Very good. What about the filter caps, such as the 80 uF vs. the 32 uF in the 18 watt Classic?

If you look at KF's designs...he selected for solid state and stiff filtration (even the Rocket got 80uF. The GZ34 can handle this, so long as it is not pushing its current limit). It goes with wanting to maximize the touch response and getting the amp to transition in and out of cleanish to output tube distortion. Now, for an 18W Liverpool, things may not just translate exactly as just-take-all-the-Liverpool-values-and-halve(or double)-them, so you might need to adjust the feel the amp depending on how you plan to run it for your playing style. For instance, you might like a little lower reservoir capacitance or want to further load the AC secondary if the amp is too "fizzy" with solid state rectification and high capacitance. This starts to get esoteric, of course.

[ViperDoc]

Thanks. I’ll likely build the full power version first and try an 18-watt version and see if I get lucky. I might not want to mess with greatness.

[wpaulvogel]

Thanks. I’ll likely build the full power version first and try an 18-watt version and see if I get lucky. I might not want to mess with greatness.

I have some custom wound Pacific transformers for 2 EL84 Liverpool amps. The power transformer is 260-0-260 200mA 6.3 6A 120 volt primary. The output transformer is 20 watts 10.4K 4,8,16 ohm. B+ idle voltage is 330 volts DC. The power transformer doesn’t have a 5 volt winding.