Blues Jr Hand Wired

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GregPlaysStrats
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Blues Jr Hand Wired

Post by GregPlaysStrats »

Hi,

Can anyone tell me what this looks like. I noticed when I bought the amp that the FAT SWITCH was missing. Took it home and opened it up to inspect thinking I might find the switch loose in the chasis. Turns out this is a "Mystery Mod" HAND WIRED who knows what.. A thread contributor at TDPRI recommended asking here as there are credible opinions to be mined here...

Thanks in advance for any information that is helpful...
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JMPGuitars
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Re: Blues Jr Hand Wired

Post by JMPGuitars »

Hi, welcome to the site.

If you want in depth details of what's going on there, you would need to draw a schematic by testing the values, and verifying what's connected to what. Most things look like spaghetti without a schematic.

That said, it's not a Blues Jr, though it does have the original transformers.

The power amp and phase inverter certainly look like a typical 18 watter. It also looks like there's a TMB tone stack? Is that correct? It's hard to tell with the layout, but I think so.

There's some interesting choices there, including how they setup the solid state rectifier. For the most part, the soldering technique looks good. Only a couple spots are not very good, but most are, so that's super.

I guess an even better question is, how does it sound?

It's also hard to tell from the photos, but it looks like the single-valve reverb method was also implemented?

The thing that would make the most sense is some variation of Zaphod_Phil's Superlite TMB with Single-Valve Reverb (available in the Downloads section). But I can't confirm that without a schematic of that build, as there are some interesting layout choices.

Thanks,
Josh
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Bieworm
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Re: Blues Jr Hand Wired

Post by Bieworm »

It looks like there are 2 parallel triodes used for 2 gain stages. This is definitely a fat sounding amp. The 2nd gain stage has its plates fed from node C , so there's more juice on that tube? This looks nothing like the SL TMB reverb that I'm building IMHO. Are you sure that's what you see Josh?
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Re: Blues Jr Hand Wired

Post by JMPGuitars »

Bieworm wrote:
Mon 07/19/21 10:09 am
It looks like there are 2 parallel triodes used for 2 gain stages. This is definitely a fat sounding amp. The 2nd gain stage has its plates fed from node C , so there's more juice on that tube? This looks nothing like the SL TMB reverb that I'm building IMHO. Are you sure that's what you see Josh?
Not at all. I see what looks like: Single channel, 18W PA & PI, SS Rec, likely a TMB with 4+1 tubes (+1 is Reverb). That's what looks like a SL TMB. Beyond that I'm not going to try and see what's feeding what, because that's the same as trying to decipher a bowl of spaghetti in a photo.

Keep in mind there are a few variations of the SL TMB (none as good as the latest in the Downloads section).

Thanks,
Josh
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Re: Blues Jr Hand Wired

Post by Bieworm »

JMPGuitars wrote:
Mon 07/19/21 11:42 am
Bieworm wrote:
Mon 07/19/21 10:09 am
It looks like there are 2 parallel triodes used for 2 gain stages. This is definitely a fat sounding amp. The 2nd gain stage has its plates fed from node C , so there's more juice on that tube? This looks nothing like the SL TMB reverb that I'm building IMHO. Are you sure that's what you see Josh?
Not at all. I see what looks like: Single channel, 18W PA & PI, SS Rec, likely a TMB with 4+1 tubes (+1 is Reverb). That's what looks like a SL TMB. Beyond that I'm not going to try and see what's feeding what, because that's the same as trying to decipher a bowl of spaghetti in a photo.

Keep in mind there are a few variations of the SL TMB (none as good as the latest in the Downloads section).

Thanks,
Josh
Thanx.. you nearly got me worried😃
Except it's 5+1 tube
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Re: Blues Jr Hand Wired

Post by JMPGuitars »

Bieworm wrote:
Mon 07/19/21 1:52 pm
Thanx.. you nearly got me worried😃
Except it's 5+1 tube
Ah, funny! I didn't notice that other tube, I was looking closely at the board. Like I said, he needs a schematic. ;)
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GregPlaysStrats
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Re: Blues Jr Hand Wired

Post by GregPlaysStrats »

Also... Am I correct in thinking this Jack is for an External Speaker and not a Footswitch? Scared to plug in a footswitch... Don't wanna' blow it up... Scared to plug in a speaker not knowing the impedance...

Again I'm grateful for any info...
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Re: Blues Jr Hand Wired

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GregPlaysStrats wrote:
Tue 07/20/21 2:54 pm
Also... Am I correct in thinking this Jack is for an External Speaker and not a Footswitch? Scared to plug in a footswitch... Don't wanna' blow it up... Scared to plug in a speaker not knowing the impedance...

Again I'm grateful for any info...
Since there is only 1 green wire coming from the OT there is only 1 impedance available. I suspect it's 8 ohm. And Yes the 2 jacks are both for speakers. So if you attach 1 speaker it should be 8 ohm. If you add another they both should be 16 ohm.. but you ain't harming anything if it's 2 x8 ohm speakers. You should avoid combining 2 x4 ohm speakers though...
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Re: Blues Jr Hand Wired

Post by Doxie man »

Looks like whoever built that knew what they were doing. It’s well made…..head and shoulders above what it was originally from Fender 👌. If it sounds good and functions well then you got yourself a good amplifier and I wouldn’t mess with it.
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Re: Blues Jr Hand Wired

Post by Doxie man »

Doxie man wrote:
Sat 08/28/21 9:28 pm
Looks like whoever built that knew what they were doing. It’s well made…..head and shoulders above what it was originally from Fender 👌. If it sounds good and functions well then you got yourself a good amplifier and I wouldn’t mess with it.
PS: secure those circuit board nuts….especially the one missing in the top left corner. Secure tightly then paint them over with a thick coat of nail polish or use blue lock-tite thread locker 👌
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Re: Blues Jr Hand Wired

Post by Bieworm »

Doxie man wrote:
Sat 08/28/21 9:31 pm
Doxie man wrote:
Sat 08/28/21 9:28 pm
Looks like whoever built that knew what they were doing. It’s well made…..head and shoulders above what it was originally from Fender 👌. If it sounds good and functions well then you got yourself a good amplifier and I wouldn’t mess with it.
PS: secure those circuit board nuts….especially the one missing in the top left corner. Secure tightly then paint them over with a thick coat of nail polish or use blue lock-tite thread locker 👌
I try to use nuts with the teflon ring most of the time. I also replace it when I loosen it every time. On other nuts it's the blue loctite I use...
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Re: Blues Jr Hand Wired

Post by ViperDoc »

GregPlaysStrats wrote:
Tue 07/20/21 2:54 pm
Also... Am I correct in thinking this Jack is for an External Speaker and not a Footswitch? Scared to plug in a footswitch... Don't wanna' blow it up... Scared to plug in a speaker not knowing the impedance...

Again I'm grateful for any info...
Those are output jacks 100%. The output is 8 ohm unless that specific transformer somehow says otherwise, usually on the bell there is some sort of make and ID code. Hammonds have nice labels with all the info printed.

Here is a useful resource if you're looking for a Fender schematic:

https://el34world.com/charts/Schematics ... matics.htm
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