Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Snake5150 on May 26, 2024, 06:30:53 pm
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Hello all, just realized my output transformer doesn’t perfectly match the schematic I’m using. It lacks a 4 ohm out from the secondary, it also has a 100v tap from the secondary.
Can someone explain.
Obviously gonna omit the 4 ohm out if need be and don’t know were the 100v wire would go. Any advice to adapt the switch to not accidentally have an unselected load upon start up would also be great. And most importantly
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100V tap would be useful in a real public address system such as a school with amp in the office and speakers in all the classrooms. Not useful at all for a guitar amp. No 4Ω tap is not the end of the world. What other taps do you have? Wanna share your amp schematic and transformer data sheet? Can't be much help with the little bit of info posted so far.
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100V tap would be useful in a real public address system such as a school with amp in the office and speakers in all the classrooms. Not useful at all for a guitar amp. No 4Ω tap is not the end of the world. What other taps do you have? Wanna share your amp schematic and transformer data sheet? Can't be much help with the little bit of info posted so far.
I don’t have the spec sheet for the ot that they specify. But I’m sure this one is of close enough value. This is the amps “schematic” and the transformer sheet that I have.
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Interesting
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I suggest to insulate off the 100V output wire, get rid of the impedance switch and fit 2 speaker output sockets, one at 8 ohms, the other at 16.
10k4 seems an bizarre primary impedance for a JTM45 OT, around 6k6 then 8k being impedances used by Marshall :think1:
The layout seems to show an unsafe arrangement for the chassis safety earth, ie the fastener used serves dual purpose, also secures the IEC inlet.
I suspect that fastener probably can't be tightened up to a high torque without splitting the IEC inlet.
I don't understand how companies that publish layouts for mains powered equipment don't feel obligated to have a competent person check them :dontknow:
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I suggest to insulate off the 100V output wire, get rid of the impedance switch and fit 2 speaker output sockets, one at 8 ohms, the other at 16.
This is great advice for dealing with the higher than expected OT impedance.
I don't understand how companies that publish layouts for mains powered equipment don't feel obligated to have a competent person check them :dontknow:
But, but, it was checked by our AI Chatbot! :BangHead:
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...after the CCP signed off :icon_biggrin:
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I suggest to insulate off the 100V output wire, get rid of the impedance switch and fit 2 speaker output sockets, one at 8 ohms, the other at 16.
This is great advice for dealing with the higher than expected OT impedance.
I don't understand how companies that publish layouts for mains powered equipment don't feel obligated to have a competent person check them :dontknow:
But, but, it was checked by our AI Chatbot! :BangHead:
My iec socket snaps in and doesn’t use anchor bolts. I was going to use the transformer lugged ground as the ground for the socket. What would be a sufficient alternative?
The cab I use is either 8 or 16 ohm (selectable) so I’ll prolly eliminate the switch as suggested. That also helps not having to nail the switch locations with the rear decal.
It’s probably not the best layout , at first about a year ago I wanted a jtm 50. Now just a finish to the project. “Triode electronics” has been zero help cuz the layout is from the internet and I didn’t buy a kit from them. I have asked multiple questions via their technical support and received no replies. The transformers were cheap what can I say. At this point I’m not worried about the amp being a replica.
Also do you guys this it’s worth setting up external bias ports and pot? Pros cons?
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My iec socket snaps in and doesn’t use anchor bolts. I was going to use the transformer lugged ground as the ground for the socket. What would be a sufficient alternative?
A transformer fastener would be extremely unsuitable.
Unfortunately I'm not familiar with the chassis you've got, hence I need you to advise what other options there are?
Electrical regs / standards / code mandate a dedicated fastener for the chassis safety earth.
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do you guys this it’s worth setting up external bias ports and pot? Pros cons?
Some folks do this. OK, fine, it's convenient for a technician.
But: Safety. You can't imagine what I've seen my own children do -- sticking various items in places around the house. I don't want anyone to be able to get to a voltage source with the cover in place.
As for an external bias pot -- all it takes is a consumer to twist a knob in the wrong direction and you've got red plates. It doesn't even have to be purposeful . . .
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do you guys this it’s worth setting up external bias ports and pot? Pros cons?
Some folks do this. OK, fine, it's convenient for a technician.
But: Safety. You can't imagine what I've seen my own children do -- sticking various items in places around the house. I don't want anyone to be able to get to a voltage source with the cover in place.
As for an external bias pot -- all it takes is a consumer to twist a knob in the wrong direction and you've got red plates. It doesn't even have to be purposeful . . .
Those are both valid points. It’ll be my amp till I croak, I just wonder if the trouble of all the design and wiring , and then faceplate decals and warning is worth the time for how often it’ll have to be done. Biasing that is. I’m not a big tube changer and don’t exactly enjoy playing with 400v very often lol.
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My iec socket snaps in and doesn’t use anchor bolts. I was going to use the transformer lugged ground as the ground for the socket. What would be a sufficient alternative?
A transformer fastener would be extremely unsuitable.
Unfortunately I'm not familiar with the chassis you've got, hence I need you to advise what other options there are?
Electrical regs / standards / code mandate a dedicated fastener for the chassis safety earth.
The chassis is an aluminum one from mojotone. I can add a solitary ground lug somewhere no biggie