I'm working on a clone of the Selmer Zodiac Twin 30, with some minor mods/improvements. Got a good schematic to work from, but I'm looking for someone who actually owns the amp to send me some pictures of the wiring layout. I've heard this amp is quite quiet and low microphonics for one with a pentode gain stage early in the preamp, and a lot of the reason for that is the layout and lead dress etc. I'm familiar with the physical separation of the preamp and power amp, to opposite sides of the chassy (genius!), but I'd like to replicate as much of the rest of the fine craftsmanship as possible.
Anyone own this amp or know someone who does? If anyone has a similar Selmer amp from that era, such as the Thunderbird or a twin 50, I'd love to see pics of those as well - even though the circuits are pretty different, I'd imagine I could learn a lot.
Anyone own this amp or know someone who does? If anyone has a similar Selmer amp from that era, such as the Thunderbird or a twin 50, I'd love to see pics of those as well - even though the circuits are pretty different, I'd imagine I could learn a lot.
I have a 1964 Croc Skin Zodiac Twin 50 in reasonable condition, if that helps?
The power amp in the 50 is different to the 30; it is fixed bias rather than cathode bias; and the power transformer itself has been replaced; and the wiring is not totally original there as a result.
I believe the preamp sections are pretty much the same between the two though; and as far as I know the preamp in mine is pretty much as original.
What would you want pics of?
Cheers, and regards,
Ant.
The power amp in the 50 is different to the 30; it is fixed bias rather than cathode bias; and the power transformer itself has been replaced; and the wiring is not totally original there as a result.
I believe the preamp sections are pretty much the same between the two though; and as far as I know the preamp in mine is pretty much as original.
What would you want pics of?
Cheers, and regards,
Ant.
Have you been through the Selmer amp website? I'd also recommend contacting one of the authors.
Selmer Truvoice Amplifiers
Selmer Truvoice Amplifiers
Ant, I would love to have pics of the wiring for both sections, especially the preamp. There's some very clear pics of the power amp layout from the link I previously commented on, but the preamp is so dense I could use some close ups at different angles.
Righty-ho.... took some photos of this ere Selmer.
Having trouble uploading them though. So I've stuck them onto Microsoft OneDrive; there's a link to them below.
Microsoft OneDrive - Access files anywhere. Create docs with free Office Online.
Mods: I know this is bad form and you'd prefer the images here so everyone can see them. So if you could advise this n00b on how to upload them, I'll do so.
Cheers, and regards,
Ant.
Having trouble uploading them though. So I've stuck them onto Microsoft OneDrive; there's a link to them below.
Microsoft OneDrive - Access files anywhere. Create docs with free Office Online.
Mods: I know this is bad form and you'd prefer the images here so everyone can see them. So if you could advise this n00b on how to upload them, I'll do so.
Cheers, and regards,
Ant.
I tried - as you will have noted above.. But the uploader just hung when I tried. Perhaps I was bouncing off some limit somewhere (size? n00b restriction? Whatever it was, there was nothing to tell me).
At least with the link they are available now.
If anyone else wants to have a go at uploading them, feel free.
Cheers, and regards,
Ant.
At least with the link they are available now.
If anyone else wants to have a go at uploading them, feel free.
Cheers, and regards,
Ant.
> Perhaps I was bouncing off some limit somewhere (size? n00b restriction? Whatever it was, there was nothing to tell me).
Noted in bottom of uploader box (you have to scroll).
Modern O/Ses (Mac, Win, Android, maybe unixes) have some tool for exporting lower-res (and filesize) images. IrfanView (utterly free, super useful) is available on Windows. Another forum has posted Image size-How to reduce it. PicResize - Crop, Resize, Edit images online for free! has been around a very long time.
Noted in bottom of uploader box (you have to scroll).
Code:
Filetype Max Filesize
bmp 195.3 KB
gif 390.6 KB
jpg, jpeg 976.6 KB
png 976.6 KBModern O/Ses (Mac, Win, Android, maybe unixes) have some tool for exporting lower-res (and filesize) images. IrfanView (utterly free, super useful) is available on Windows. Another forum has posted Image size-How to reduce it. PicResize - Crop, Resize, Edit images online for free! has been around a very long time.
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I have plenty of tools to crop / resize / whatever. And agreed - just because I have a camera, doesn't mean I know how to use it. Never pretended otherwise, and I'd be the first to admit it: I'm a software engineer by trade, not a photographer, and have little interest in photography per se. And in the absence of any dialog that said what the forum jpg uploader was barfing on - it just hung - I settled for posting a link so that at least the OP could get access to the photos that I dismantled one of my vintage amps to take for him / her. Which was the primary goal.
Seems that sir pTerry is alive and well: "No good deed goes unpunished".
And this will be my last word on my photo uploading woes - whether they were self-inflicted or otherwise.
Cheers, and regards,
Ant
Seems that sir pTerry is alive and well: "No good deed goes unpunished".
And this will be my last word on my photo uploading woes - whether they were self-inflicted or otherwise.
Cheers, and regards,
Ant
These are excellent pics, Ant, much obliged! Very thorough. Between this and the other links folks posted, I should have what I need.
Doing my best to attach them here. I used bulkresizephotos.com reducing them to 20% of their original size, as some of them were around 3.5 Mb, to get them below the limit for JPEG's. Surprisingly, they all came out as less than 80 Kb! Even more surprisingly, they're still plenty large with good resolution. Here's hoping they come out well below:
Doing my best to attach them here. I used bulkresizephotos.com reducing them to 20% of their original size, as some of them were around 3.5 Mb, to get them below the limit for JPEG's. Surprisingly, they all came out as less than 80 Kb! Even more surprisingly, they're still plenty large with good resolution. Here's hoping they come out well below:
Attachments
Nice job on the posting of the images. Looks like it was the resize that I was missing; many thanks to you for sorting. 
Hopefully the images you have are good enough that you can zoom into the details you want / need.
If I can help you further with any info for your build, then of course feel free to ask; happy to help if I can. I wish you good luck with your project - doesn't look the easiest thing to clone 50+ years later!
Cheers, and regards,
Ant.
Hopefully the images you have are good enough that you can zoom into the details you want / need.
If I can help you further with any info for your build, then of course feel free to ask; happy to help if I can. I wish you good luck with your project - doesn't look the easiest thing to clone 50+ years later!
Cheers, and regards,
Ant.
I think the amount of pictures you took should be more than sufficient for me to get what I need! not the easiest, no, but certainly not the toughest, and i'm going to simplify quite a bit. only going to include the second channel, for one thing, and can hopefully simplify the tone selector into some sort of custom 6-way switch.
i think it'll be well worth it. this amp has tone worth obsessing over, and I should be able to make it for about a third or at least half of what a real one goes for!
i think it'll be well worth it. this amp has tone worth obsessing over, and I should be able to make it for about a third or at least half of what a real one goes for!
It might be sacrilegious to say this, but... i never much cared for the fixed tone shapes from the pushbuttons; they sound a bit too much like a "cocked wah pedal" to me. I found the regular rotary tone control to be more usable.
But the tremolo is very nice (and that magic eye...!), and there is something particularly pleasing about the gentle compression that the 50W tube-rectified output brings to the party when playing clean.
Good luck!
Cheers, and regards,
Ant.
But the tremolo is very nice (and that magic eye...!), and there is something particularly pleasing about the gentle compression that the 50W tube-rectified output brings to the party when playing clean.
Good luck!
Cheers, and regards,
Ant.
Damn! I was looking around the web for a possible turret board layout.. alreasy have a Selmer Treble and Bass mk II, but have also been obsessing over exactly these amps. It's my dream amp. Rarely pops up locally in the 30W version.
Can I pick your brain about your making of this amp?
Bump - finally have time to tackle this beauty!
I have most of the components sussed/acquired, but am getting a bit hung up on the OPT. This schematic says 6.5K into 16, and also shows a tap for the screens through 1K resistors, but doesn't say what the tap is at... I've seen some people online saying that they actually used an ultralinear transformer here, in pursuit of better cleans, which would explain the tap! But I've seen others who claim it's the exact same OPT as the one from the Marshall JMT45, which would put it at more like 7.3K primary impedance, and no tap...
Anyone out there with a twin 30 who's able to get their OPT's part number, or possibly take some measurements/pictures for me? If you can even just check how many wires are coming from the primary side, I'd be very grateful.
I'd also appreciate (in case no one can provide info from the source) anyone who can help me guess at where the screens should be tapped from (i think ultralinear is like 40%?) and advise on which hifi transformers might be appropriate. My gut feeling is that this actually IS an ultralinear, as it's quite hard to find a classic guitar amp OPT with this high primary impedance at an appropriate wattage rating; the Hammond 1750Q, which is a direct replacement for the JMT45's OPT, seems to be quite the exception! But there are plenty of hifi OPT's available at even higher primary impedance values, and both the 1650P and 1650PA seem to fit the bill.
Some of the folks who say it's got an ultralinear transformer claim that it is likely partially responsible for the "woofy", unsubstantial bass when the amp is heavily overdriven. I'd love if anyone could comment on the potential effects of changing this setup to supply the screens from the main power rail at the same voltage (which I think should be about 7-8V less than the plates). Not having to get a hifi transformer could save me some dough, and having solid, clear bass is pretty important to me as a rhythm guitarist, but I don't want to stray TOO far from the original design - I want this amp to sound at least 90% original, so if this would be a drastic change I'd rather keep it the same. I wanna appreciate it for what it is!
Keep in mind, this amp is biased hot as hell, 2 EL34's in push-pull that are ALMOST in true class A... UNH my mouth waters every time I think about it hahahahaha
Ah, one more random question - what current rating would y'all have on the high voltage winding of the power transformer, in light of that? I was thinking 250mA per side would be ok.
Cheers! Can't wait to share pics once I've started!
I have most of the components sussed/acquired, but am getting a bit hung up on the OPT. This schematic says 6.5K into 16, and also shows a tap for the screens through 1K resistors, but doesn't say what the tap is at... I've seen some people online saying that they actually used an ultralinear transformer here, in pursuit of better cleans, which would explain the tap! But I've seen others who claim it's the exact same OPT as the one from the Marshall JMT45, which would put it at more like 7.3K primary impedance, and no tap...
Anyone out there with a twin 30 who's able to get their OPT's part number, or possibly take some measurements/pictures for me? If you can even just check how many wires are coming from the primary side, I'd be very grateful.
I'd also appreciate (in case no one can provide info from the source) anyone who can help me guess at where the screens should be tapped from (i think ultralinear is like 40%?) and advise on which hifi transformers might be appropriate. My gut feeling is that this actually IS an ultralinear, as it's quite hard to find a classic guitar amp OPT with this high primary impedance at an appropriate wattage rating; the Hammond 1750Q, which is a direct replacement for the JMT45's OPT, seems to be quite the exception! But there are plenty of hifi OPT's available at even higher primary impedance values, and both the 1650P and 1650PA seem to fit the bill.
Some of the folks who say it's got an ultralinear transformer claim that it is likely partially responsible for the "woofy", unsubstantial bass when the amp is heavily overdriven. I'd love if anyone could comment on the potential effects of changing this setup to supply the screens from the main power rail at the same voltage (which I think should be about 7-8V less than the plates). Not having to get a hifi transformer could save me some dough, and having solid, clear bass is pretty important to me as a rhythm guitarist, but I don't want to stray TOO far from the original design - I want this amp to sound at least 90% original, so if this would be a drastic change I'd rather keep it the same. I wanna appreciate it for what it is!
Keep in mind, this amp is biased hot as hell, 2 EL34's in push-pull that are ALMOST in true class A... UNH my mouth waters every time I think about it hahahahaha
Ah, one more random question - what current rating would y'all have on the high voltage winding of the power transformer, in light of that? I was thinking 250mA per side would be ok.
Cheers! Can't wait to share pics once I've started!