Amp ideas

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Riffmonster
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Amp ideas

Post by Riffmonster »

Hi all,

It has been a while since I last posted here. Unfortunately, I just did not have much time to work on amps but I still managed to build two 50 watt plexis over the last months. Anyways, I want to use some spare parts for an amp but I am unsure what to build.

1. I have an PT that has a 230V 130mA secondary and it also has another secondary with 20V 130mA, which can be connected in series with the first secondary and then would give me 250V. The 6.3V tap has 4A.
2. I also have an 18 Watt 8k output transformer.

So, my question is: what should I build? Does it make sense to run two EL84 at a plate voltage of about 300-320V or will it sound bad? Should I look into using other tubes? In any case, I would prefer a rather simple amp, maybe with a Vox, Matchless or Trainwreck flavor. What do you think? Any suggestions would be great.

Best wishes,
Simon
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Bieworm
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Re: Amp ideas

Post by Bieworm »

Riffmonster wrote:
Wed 05/22/24 3:46 am
Hi all,

It has been a while since I last posted here. Unfortunately, I just did not have much time to work on amps but I still managed to build two 50 watt plexis over the last months. Anyways, I want to use some spare parts for an amp but I am unsure what to build.

1. I have an PT that has a 230V 130mA secondary and it also has another secondary with 20V 130mA, which can be connected in series with the first secondary and then would give me 250V. The 6.3V tap has 4A.
2. I also have an 18 Watt 8k output transformer.

So, my question is: what should I build? Does it make sense to run two EL84 at a plate voltage of about 300-320V or will it sound bad? Should I look into using other tubes? In any case, I would prefer a rather simple amp, maybe with a Vox, Matchless or Trainwreck flavor. What do you think? Any suggestions would be great.

Best wishes,
Simon
You might want to look t the use of 6AQ5 tubes. They’re miniature tubes that resemble 6V6 characteristics. You could build a 6V6 plexi, or something totally different. The 230V secondary is plenty in that case. 6AQ5’s want between 250 and 300V on the plates

They’re dirt cheap for NOS and sound awesome!! I have a tweed bassman circuit running EL90’s, which are a kinda 9 pin 6AQ5 version
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Riffmonster
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Re: Amp ideas

Post by Riffmonster »

Thanks for the quick reply, nice idea! I actually still have a lot of 6P1P-EV tubes at home (which are the same like EL90s, I think) The PT would work perfect for them but from what I gather these tubes usually work with a 10-12K primary of the OT. Did you try using these tubes with a 8k 18 watt OT in the past? Maybe I should just try that…
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Re: Amp ideas

Post by Bieworm »

Riffmonster wrote:
Thu 05/23/24 2:14 am
Thanks for the quick reply, nice idea! I actually still have a lot of 6P1P-EV tubes at home (which are the same like EL90s, I think) The PT would work perfect for them but from what I gather these tubes usually work with a 10-12K primary of the OT. Did you try using these tubes with a 8k 18 watt OT in the past? Maybe I should just try that…
yes I did. I rewired a Tremolo TMB once to accommodate 6P1P-EV tubes (those are the ones I use when I propose 6AQ5) ad I was impressed. You should know that the max plate voltage on those is supposed to be 275V, but I run mine near 300V. I do have a switch that lowers the B+ in case I have to play for several hours in a row. But it just sounds better with the higher plate voltage. I shouldn't recommend this even though I WTF'it myself. :D
If you want to secure your transformers you can always add a fuse on the high voltage ground wire.
I attached the schematic from Josh, which I adapted to run 6P1P tubes.
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Riffmonster
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Re: Amp ideas

Post by Riffmonster »

This is great, thank you!! I will go with my 18 Watt transformer and try the 6P1P-EV. I can always drop the voltage with zeners if it’s too high. Let‘s see which pre amp circuit I will use, I will keep you posted here!
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Re: Amp ideas

Post by JMPGuitars »

Bieworm wrote:
Thu 05/23/24 2:44 am
You should know that the max plate voltage on those is supposed to be 275V, but I run mine near 300V.
Go look at the datasheet for EL84s and see what the max is then compare it to every 18W variant. 😉
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Bieworm
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Re: Amp ideas

Post by Bieworm »

JMPGuitars wrote:
Thu 05/23/24 8:07 am
Bieworm wrote:
Thu 05/23/24 2:44 am
You should know that the max plate voltage on those is supposed to be 275V, but I run mine near 300V.
Go look at the datasheet for EL84s and see what the max is then compare it to every 18W variant. 😉
I know. Most run EL84 about 50V higher than the 300V max spec. The 6P1P EV is rated at max 250V, so I reckon 300V will be fine. Pushing it to 345V makes me nervous 😎
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Dimi Pana
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Re: Amp ideas

Post by Dimi Pana »

Hello all!

This is my very first post in this forum, and I'm not even sure if I should have posted here or elsewhere, please redirect me accordingly.

I'm a recently retired (born mid-50s) and looking to get into diy amp building. I am not an electronics expert but know enough to be ..."dangerous". I'm also a mediocre guitar player, but good enough to strum/sing lullabies to my grand children.

I have a very specific question:

I'm interested in building a simple 18-watt amp, and simple is my intended M.O. I'm looking for the simplest version available that if built well will produce decent results. I am also not looking for a two channel/reverb/tremolo-etc. design. A one input, no effects, 18w amp would be perfect for what I need. A clean, good, trusty schematic, with hopefully a BOM and easy to find parts (or alternatives) is what I'm looking for. I wouldn't mind though if the design had an (add-on) effects loop (as a mod).

Is there such an amp/design which can still be faithful (given the limitations) to the original 18w sound?

I apologize if my post is somewhat ..."sacriligious" to all enthusiasts who strive for historical accuracy in their builds, I understand ... I might have crossed the line here. Still, I'm interested in your ideas, comments, feedback.

Thank you for taking the time to do so!
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Re: Amp ideas

Post by Bieworm »

Hi there. Check the lite2b in the download area. viewtopic.php?t=24431
It’s the perfect starter build amp. And it sounds tremendous!!!
Maybe Josh has a BOM?
Where are you from?
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Re: Amp ideas

Post by JMPGuitars »

I agree, the Lite 2b(ish) is the best option. I don't have a BOM for it, but look at the BOM for the Tremolo TMB Reverb and you'll see links to parts I like on Mouser, just find the specific values you need. It's not that hard, there aren't a lot of parts in the amp.

You can also copy the effects loop from the Tremolo TMB and use it in the Lite 2b(ish).

Review the soldering thread and videos in my signature to brush up on your skills.

Thanks,
Josh
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Dimi Pana
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Re: Amp ideas

Post by Dimi Pana »

Thank you Josh and Bieworm; I will definitely follow your suggestions. Is it OK if I post back here? I'm pretty new and my questions will be rudimentary (but I'll keep it short and sweet, promise). I was born in Greece but been permanently living in the US since 1987 (first Boston, now NW burbs Chicago). Thanks! Hi-ya
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Re: Amp ideas

Post by Dimi Pana »

I just finished browsing and downloading everything in the suggested topic e.g. viewtopic.php?t=24431

I suppose the main 3 items are the JMP uploaded PDFs (Schematic, layout and voltages).

Everything else is there as a possible improvement/upgrade and more of a suggestion for the builder, but not a "must-do" (mod or add-on), correct!?

Btw, there is a BOM compiled by 'Ramiro'; from a quick look it appears to be very close or at least a good starting point.

Lastly, I'm including a 'cut-off' of the FX loop from the trem schematic. I see that the 'send' and 'return' points are on either side of that 68K resistor. Question is, that resistor is part of the main circuit or added with the FX loop?!

Thanks for your input so far, let me absorb and I'll be back!
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Re: Amp ideas

Post by JMPGuitars »

Dimi Pana wrote:
Fri 05/24/24 5:05 pm
Thank you Josh and Bieworm; I will definitely follow your suggestions. Is it OK if I post back here? I'm pretty new and my questions will be rudimentary (but I'll keep it short and sweet, promise). I was born in Greece but been permanently living in the US since 1987 (first Boston, now NW burbs Chicago). Thanks! Hi-ya
Start your own thread and ask your questions there.
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