High Voltage Hijinks
- Thread starter Hal Harvey
- Start date
Hal Harvey
Well-known member
Jeez! Almost there though. Mercury Magnetics seems to take around the same time for a made-to-order, non stocked set. A little over 6 weeks for the T set. I looked back in my email, the GT120 set were sent out 2 weeks after, ordered during the holidays, maybe they had a set on hand though.
I'd rather use something readily available but the T and GT/OR120 transformers are pretty unique and no one else makes clones of them. I think I am done building clones++ though (aside from a Trainwreck haha). I don't think I need a Hiwatt, and Fender + Marshall transformers are very well covered by winders like Heyboer, cheaper, and actually stocked.
Hal Harvey
Well-known member
I'm actually working on the T in anger finally 
Rectifier & reservoir board, heater elevation and balance board, bias board in the back. Chassis mounted power tubes cathode fuse and led in the shot too.
Output transformer protection MOVs and flyback diode board.
Rectifier & reservoir board, heater elevation and balance board, bias board in the back. Chassis mounted power tubes cathode fuse and led in the shot too.
Output transformer protection MOVs and flyback diode board.
Asdrael
Well-known member
Man if I had access to decent quality OT at a good price here I would be happy. I am paying less for a custom made high quality OT than a regular Hammond for which I have to compromise my specs (either not the right primary, or only 1 secondary). And since I am ordering custom OT I just go custom PT too so I can get the windings I like.
That's a step up in quality again good job! Ready to take the plunge to a DC heater setup now? There is a adaptor board for a RECOM available
Hal Harvey
Well-known member
That's a step up in quality again good job! Ready to take the plunge to a DC heater setup now? There is a adaptor board for a RECOM available
I do have a 12V RECOM on hand (for relays for a Dumble ODS build). I wire the heaters Soldano style and elevate the heaters - I've never had heater noise. I think there's just tons of bad lead dress, chassis layouts, and/or PCB layouts in the guitar amp world. I would go DC for heaters if I had relays in build, and will likely DC heat the preamp tubes in the ODS build.
I think if was doing PCBs for tube amps I'd go modular. Only things that need to be near the tubes on the PCB with the tube sockets would be on there. Like grid stoppers. The plate resistor in a driver-follower tube. That kind of thing.
Guardians of the analog
Papi Fuego
I added a 3 way bright switch to my dirty Shirley build. This little switch turned a great amp into a super versatile tone machine. Center is off for stock JTM vibes. 100pf gives more plexi type vibes and 1n for more aggressive JCM era grind.
Then I started tinkering with the footswitch jack. The original amp had a 2 button switch for boost and the effects loop. The footswitch is wired different than the replacement boards so I had to figure out what the tip and sleeve connected to on my build. Since I leave the effects loop always on i focused only on the boost. The boost on this is a higher gain range. It adds a 3.3k and 680n in parallel with the 10k cold clipper (classic 2203/04 mod). It's on a push pull pot on the gain pot. I repurposed everything needed to make a remote footswitch. Used a @szukalski relay and it works perfectly. Now the amp has 2 gain modes, V2a cathode 680n bypass cap, 3 way bright switch and Jose style clippers all on switches/push-pull pots. Most versatile 1 channel amp I've ever had.
Then I started tinkering with the footswitch jack. The original amp had a 2 button switch for boost and the effects loop. The footswitch is wired different than the replacement boards so I had to figure out what the tip and sleeve connected to on my build. Since I leave the effects loop always on i focused only on the boost. The boost on this is a higher gain range. It adds a 3.3k and 680n in parallel with the 10k cold clipper (classic 2203/04 mod). It's on a push pull pot on the gain pot. I repurposed everything needed to make a remote footswitch. Used a @szukalski relay and it works perfectly. Now the amp has 2 gain modes, V2a cathode 680n bypass cap, 3 way bright switch and Jose style clippers all on switches/push-pull pots. Most versatile 1 channel amp I've ever had.
pbrommer
Well-known member
Awwww yeah. 3 stages of 2k7/.68uF with a 56k on the cathode follower into the tone stack is balls to the wall awesome. Play all the hard rock riffs.
JohnnyCreepy
Well-known member
And here I’ve been wondering this whole day if I should go back to +20uF bypass caps just to make sure nothing unwanted leaks back to signal chain!
Different topologies, different needs!
Guardians of the analog
Papi Fuego
Here's a sound clip of the feral cheryl with the bright cap in a mix. Gibson SG with low output PAFs boosted with my Uber Driver.
Paradox916
Well-known member
Sounds awesome man! Punchy and full, nice stereo panning as well.
Guardians of the analog
Papi Fuego
Hal Harvey
Well-known member
All the turret boards are done:
On to wiring. I'll likely go heaters>bias system>power tubes>install transformers>power supply>pre and pi.
On to wiring. I'll likely go heaters>bias system>power tubes>install transformers>power supply>pre and pi.
Asdrael
Well-known member
Wow that's nice. Very present with body, really everywhere on the spectrum.
Man as I said before, you really stepped up your game. Looks clean as hell. Funny spot for the fuse on the top by why not
Will you be building a headshell for this, or leaving it open?
Hal Harvey
Well-known member
Man as I said before, you really stepped up your game. Looks clean as hell. Funny spot for the fuse on the top by why not
Thank you!
Fuse on top is power tube cathode fuse with led indicator. I had originally planned for one for each tube but Merlin states this can cause some ill effects for the OT so I changed to having just the one. I probably could have moved it to the rear at that point but I like the idea of it being physically close to the tubes.
I have to build head cabs for all of these haha. I picked up a nice dovetail jig etc. I’ll likely go with furniture grade wood and stain rather than tolex.
Paradox916
Well-known member
Super clean layout
Feral Feline
Well-known member
Yeah, ultra-classy...
...makes me think I should ask for your layout of the Hilbish.
That's kind of like ...
... thinking if I get a synth and some Moog Taurus pedals and a Geddy Lee Signature Jazz Bass that I'll then be able to do what Lee does.
Well, apart from the vocals...
Even if I had your Hilbish layout...
Geeze I've been putting a LOT of ellipses in my posts lately...
...makes me think I should ask for your layout of the Hilbish.
That's kind of like ...
... thinking if I get a synth and some Moog Taurus pedals and a Geddy Lee Signature Jazz Bass that I'll then be able to do what Lee does.
Well, apart from the vocals...
Even if I had your Hilbish layout...
Geeze I've been putting a LOT of ellipses in my posts lately...
Hal Harvey
Well-known member
Yeah, ultra-classy...
...makes me think I should ask for your layout of the Hilbish.
That's kind of like ...
... thinking if I get a synth and some Moog Taurus pedals and a Geddy Lee Signature Jazz Bass that I'll then be able to do what Lee does.
Well, apart from the vocals...
Even if I had your Hilbish layout...
Geeze I've been putting a LOT of ellipses in my posts lately...
I'm really flattered by the praise. I don't think my GT120 layout is in the same league as the Model T layout. I was pretty rusty when I did it, I would definitely tweak if I was going to make that amp again, maybe even start over. I was also in the position of working within the constraints of that chassis, which is an awesome clone of the original, but still, I wanted to some extra stuff and I had to shoe horn it in (quad power tube bias, MOVs on mains power, MOVs on OT, both sides the B+ secondary fused, etc).
I've also since made changes. Originally I planned to have three mods: EQ lift, some changes to the PI (which I made permanent), and a global NFB switch (stock, none, less). The EQ lift adds quite a bit gain. I ditched the global NFB switch added a local negative feedback mod. What it does is you have three options, stock (of course), some LNFB on the 2nd gain stage, and third option is LNFB on both gain stages with more on the 2nd then before. The LNFB essentially makes it harder to cause those gain stages to distort, you lose some gain, but instead of distortion you get compression. The LNFB makes it easier to have more power tube distortion present because you are getting more headroom in the preamp and hitting the power amp side with a cleaner signal. The LNFB mod really feels like it's in the spirit of the amp as a doom machine because you can just slam the frontend HARD with fuzz and the LNFB sweetens it nicely. Here's an example of the LNFB setup in a Dumble ODS:
On the 2nd stage... The 0.05uf coming back to the grid from the plate through a 22M resistor. The 220K at the grid is the 3rd piece of the puzzle and needed for it work property. Merlin has a chapter on it in his old Guitar and Bass Preamp book with gain calculations etc., I don't know if it's in the new book, I'll have to look. I don't remember where I ended up for values but I tweaked until happy.
I absolutely love the GT120!!! I'm excited to run the Model T with it in parallel.
@Feral Feline If you decide you want to go down making a turret board I will dig up my layout if you want to use it as a starting point.
Last edited:
Harry Klippton
Not Interested
Asdrael
Well-known member
Rare soldering stock image where the guy doesn't hold the iron by the tip. Well played.