Non-Traditional 15 watt Liverpool with PCB

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RJ Guitars
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Non-Traditional 15 watt Liverpool with PCB

Post by RJ Guitars »

Hello amp builders. Some of you have been expecting me to post up info on a PCB Liverpool build, similar to the PCB Express that a few of you worked up with me. I have been working on that amp for the last couple weeks and it all looks good. I made some updates on the PCB board so that I could get both the Express and Liverpool using the the same PCB and added a few other features as well. The boards arrived and I've been working up a Liverpool but with a half power layout.

This is also the same chassis that I use for the express amp with some subtle mods to accommodate the 15 watt transformer set. On the Express I punched out the power tubes to octal size. I had the shop make up the original chassis for these anticipating the Liverpool build and noval output tubes. I had the Edcor folks wind a custom set of transformer for me with the EL84 tubes in mind. Power trans is 270-0-270 and the output is 8.1K primary. Edcor has a policy that they do not do multiple secondaries on the output of their 15 watt transformers but in this case I was able to persuade them to make some up just for me. They are typical Edcor Blue and look great!

More info to come...

rj
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fishy
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by fishy »

RJ,

Cool...... as always.

What is the story with the chassis. Seems to be some extra hardware holding the top on.......
Now, the pcb seems to be on display in the Express thread..... a quick peek at that shows some extra "stuff" around that spare triode...
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by RJ Guitars »

fishy wrote:...What is the story with the chassis. Seems to be some extra hardware holding the top on.......
For the story on that you'll have to go to the beginning of the post on the older sibling Express amp - http://ampgarage.com/forum/viewtopic.php?t=17524 but basically that involves a "reinvestment" of a bad idea I had in chassis design.

I've added a progress photo of some of the wiring that I did before I dropped the PCB board into place. So far I have kept this build simple and basic because I don't want to try too many "improvements" until I verify that my PCB board updates and other design ideas are going to work. I did deviate from the norm on my heater wiring with a tight twist and a little less conventional approach to routing the leads to the #9 pin on the preamp tubes.
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M Fowler
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by M Fowler »

Looks good rj and good idea building low powered amps.

Mark
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RJ Guitars
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Printed Circuit Board Liverpool

Post by RJ Guitars »

I have this about 95% finished now. I did not add the presonance or the line out features because I wanted to make sure the amp worked first. It indeed works and it works well. For now I am going to say it sounds good but there is still room for improvement. I really havn't made many changes to the traditional Liverpool circuit except for the transformer set and the output tube bias resistor... I also only used one value for a brite cap - a 47pF. It does not have any squeal or weirdness but does seem like it's close to the stability edge when I engage the brite switch. It's loud but noticeably less loud than the Express. It's still early in this effort and I want to play the amp for a while then start thinking about tweaks.
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Last edited by RJ Guitars on Mon May 28, 2012 10:20 pm, edited 1 time in total.
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Reeltarded
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by Reeltarded »

That was fast. :)
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RJ Guitars
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by RJ Guitars »

Reeltarded wrote:That was fast. :)
...deceptively fast. It was finished when i started the post. I just didn't want to start at the ending and it took a bit of effort for me to figure out how to make this interesting and worthwhile for folks. There is also not a lot that is different from the Express version so I wanted to get down to the important stuff rather than reproduce the same general fabrication details.

Having said all that, these do go together pretty fast and it was also obvious that the wire use is minimal. The heaters take the most with 18 gauge stranded (teflon). I used the leads that I cut off from the transformers for most of the AC & power circuits and then used 20 gauge solid copper (PVC) wire for much of the rest of it.

I think the story or at least the educational part of this build for me is going to be sorting out how to make the 2 tube Liverpool circuit sound it's best.

I've got cost info sorted out for anyone that wants to put a LP or XP together based on these same parts... TAG guys get a discount of course.

rj
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by paulster »

Neat job. Just one immediate observation is that I'd not have the output tube cathode resistor on the front panel when using a plastic control overlay as the heat will likely cause it to try to lift and you may end up with it looking a bit warped in time.

This is a great idea though.
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by dorrisant »

Great job, rj! Looks beautiful.

Just a suggestion... this new amp and the pcb Express (possibly with the same pi values) in a head to head clip comparison...?

I'm digging the pcb revisions.

paulster... I think that is the power supply resistor on the inside of the front panel... the cathode resistor is on the board next to the electrolytic. Maybe that is what you meant though.

Tony
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by Bob S »

Very Very Cool RJ.
All I need now is the time & money to partake.
Well Done Sir!
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by RJ Guitars »

dorrisant wrote:...Just a suggestion... this new amp and the pcb Express (possibly with the same pi values) in a head to head clip comparison...?Tony
Yes that is a good plan... right now I think the Express would totally dominate in all categories. I did not make any changes to the traditional Liverpool circuit except for the transformer set and the bias resistor... which is actually a lot to change. I think this LP circuit needs to be optimized for the 2 hole output.

My first observation on this amp is that it goes from clean to mean more abruptly than the Express and also I think it is too mean when you dial it above noon. My first inclination would be that the output section is getting hit too hard... there is still work to do before this one is ready for prime time. It sounds good and doesn't do anything bad, it's just not as toneful or versatile as the Express version... yet. We don't want to just have instant success here anyway. We need to learn something the old fashioned way and expect some pain and confusion before the answer just pops up... blah blah blah etc..
dorrisant wrote:paulster... I think that is the power supply resistor on the inside of the front panel... the cathode resistor is on the board next to the electrolytic. Maybe that is what you meant though.Tony
yes that's the power resistor.... which will get hot... and yes that is a plastic faceplate... which is OK and looks cool but I used it in this case because it was an unclaimed orphan. The plastic faceplates have not turned out to be extremely popular and you can see where this one warped a bit when it was laser etched. Maybe the heat from the big resistor will heal it... probably not! So once this is really making the sounds I am looking for and is worthy, It might get a new faceplate, especially if it gets hot under that resistor.

rj
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by paulster »

RJ Guitars wrote:
dorrisant wrote:paulster... I think that is the power supply resistor on the inside of the front panel... the cathode resistor is on the board next to the electrolytic. Maybe that is what you meant though.Tony
yes that's the power resistor.... which will get hot... and yes that is a plastic faceplate...
Of course you guys are right. I was clearly half asleep when I typed that. At least I knew it was the one that was going to get hot though!! :roll:
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by fishy »

My expereince with two hole Liverpools is they tend to be have a more pronounced midrange and do get dirty really quickly especially with a humbucker. Both were without a bright switch.

I did have a pretty small OT for one of those and a decent sized Hammond on the other. The Hammond was a bit crisper but still needed dropping to get some control on the clean to mean and had the same overall signature.

This is the link to the one of them (baby OT) with some info on what is in it.
The clip is with a LP. R7 is down at 39k.......

http://ampgarage.com/forum/viewtopic.ph ... =liverpool
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by rock_mumbles »

Nice rj!

and nice 2-holer pics and clip in the other thread fishy!

Have you considered trying a split-load plate on the PI for the 2-hole Liverpool?

I've seen them on a couple of lower wattage wreckish amps to keep the PI from overwhelming the output section ...
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Re: Non-Traditional 15 watt Liverpool with PCB

Post by rock_mumbles »

So I got my PCB and OT from rj yesterday.

I probably won't get to the building stage for a while, I need to finish another project, vacation, and plan things out first.

I've read that the 1k screen supply resistor is a key part of the Express/Liverpool amp ...

So I have a question, since I'm building a 2 x EL84 amp shouldn't the 1k screen dropping resistor be increased to a 2k resistor so the amp responds the same, has the same voltage drop etc.?
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