Jtm 45 jack question

[Snake5150]

In the attached layout are the input jacks viewed from the rear ?

Does anything look super strange, I’m using a different ground scheme the Hoffman one.

Were is the board “ main ground wire”?
As there are 3 wires that go to ground

Also my build doesn’t use a switch for the 8/16 ohm outs. So  I would run the 8 and 16 trans out respectively to the tips of each jack. And then ground and common to the others? After this should I have continuity to ground throughout the jack with or without a cable inserted?

[shooter]

jacks "appear" to be drawn from rear, get the datasheet for the jacket to verify
the pre-amp ground is the wire along the back of the pots, it's terminated AT the input jacks ONLY


search this forum for output jack wiring, see if you can find your answer.
you can use 2 jacks, tip gets signal, both grounds to common, BEWARE guitarists can't READ when setting up on-stage 

[Snake5150]

I figured out that I had shorting cliff jacks and had them wired wrong. In this dual jack set up should one jack be shorted when the other is connected. So that way either the 8 or 16 ohm tap is connected but never both?

[Willabe]

In this dual jack set up should one jack be shorted when the other is connected. So that way either the 8 or 16 ohm tap is connected but never both?

No!

That will kill the OT.

You don't need shorting jacks with the set up you want, or just don't wire up the shorting part. If you short to ground any of the OT taps your shorting a part of the whole secondary wind.

Just be careful to make sure you always have a speaker plugged in.

[mresistor]

I'm curious.  Why not use an impedance switch for your speaker out put? If you have two jacks there then one could be used for the impedance switch.

[Snake5150]

I'm curious.  Why not use an impedance switch for your speaker out put? If you have two jacks there then one could be used for the impedance switch.

The ot trans only has an 8 and 16 ohm out. Didnt see the point for a switch when it’s one or the other.

So wire the jacks to NOT short ever. And that being open won’t kill the ot?
Can someone explain. I thought that was transformer execution 101.

And as far a NFB the loop would go on the 8 jack.

[mresistor]

Yes. DO NOT wire either speaker jack to short to ground!   I had a deluxe reverb build wired that way for a while and decided to just put a switch in there.  So much nicer and there is a cheaper one available now to fit the bill perfectly.  I suppose with a 3 position switch you would worry about it being placed into the open position accidentally. Well with two speaker jacks, one for each impedance, you run the risk of damaging the OT with excessive flyback arc over voltage if no speaker is connected. 


If you use a 3 position switch you can wire a 100 ohm 5 watt resistor to the non used ouput position to protect the amplifier if it ever gets inadvertanly switched to the 4 ohm ( not used) position.


Here's the switch I'd recommend  https://www.tubesandmore.com/products/switch-rotary-1-pole-3-position-0


I think I'd wire the feedback to the 16 ohm jack. Not really sure on that someone will correct me most likely if it's wrong.

[Snake5150]

Yes. DO NOT wire either speaker jack to short to ground!   I had a deluxe reverb build wired that way for a while and decided to just put a switch in there.  So much nicer and there is a cheaper one available now to fit the bill perfectly.  I suppose with a 3 position switch you would worry about it being placed into the open position accidentally. Well with two speaker jacks, one for each impedance, you run the risk of damaging the OT with excessive flyback arc over voltage if no speaker is connected. 


If you use a 3 position switch you can wire a 100 ohm 5 watt resistor to the non used ouput position to protect the amplifier if it ever gets inadvertanly switched to the 4 ohm ( not used) position.


Here's the switch I'd recommend  https://www.tubesandmore.com/products/switch-rotary-1-pole-3-position-0


I think I'd wire the feedback to the 16 ohm jack. Not really sure on that someone will correct me most likely if it's wrong.

I have a rotary switch which I had planned on using before I realized the ot was only 8/16.  Which I do have room for in the chassis.
The rotary switch doesn’t go to ground on the un connected positions I’m assuming? I don’t understand how that’s not an open circut on the ot. I totally believe you but am just curious as this is my first build

[shooter]

I totally believe you but am just curious as this is my first build

so, keep it simple, pick ONE, 8 or 16, wire 1 jack, then after you've played til it's tweaking n tuning time  consider a 2nd jack.


you can "pre-drill" the future holes.  on a 1st build you want simple, complex just adds, well complexity 

[mresistor]

I agree with Shooter to start by keeping it simple on a first build. Use only one output jack and wire the OT output lead with the impedance that matches your speaker cabinet impedance.   I suppose you have a regular JTM45 style impedance switch.  If you plan your build out like Shooter says you can drill the hole for it and install it later and then could go over the wiring of the switch.

[Willabe]

So wire the jacks to NOT short ever.

Yes don't use the shorting connection.

So wire the jacks to NOT short ever. And that being open won’t kill the ot?

Not as long as you have a speaker hooked up to 1 of the jacks. And no you can't plug an 8 ohm speaker into the 8 ohm jack AND plug a 16 ohm speaker into the 16 ohm jack both at the same time.  You can only use 1 speaker jack at a time. 

The secondary of the OT is just wire wound around the iron core lams. Lets say, and this is not the true number, but, they wound 10 winds around the core and without cutting it they just cleaned the enamel insulation off of that wire and soldered in a wire fly lead, ie a tap, for the 8 ohm load, then they wound another 10 turns and soldered a fly lead to the winds end as the 16 ohm lead load.

So it's 1 continuous wire that is 'tapped' at a certain point. If you have 2 jacks hooked up to the 2 different ohm leads and you ground either 1 the whole wind is being grounded because the secondary wind is 1 wire. Ground the secondary, no signal goes to the speaker.

[Snake5150]

So wire the jacks to NOT short ever.

Yes don't use the shorting connection.

So wire the jacks to NOT short ever. And that being open won’t kill the ot?

Not as long as you have a speaker hooked up to 1 of the jacks. And no you can't plug an 8 ohm speaker into the 8 ohm jack AND plug a 16 ohm speaker into the 16 ohm jack both at the same time.  You can only use 1 speaker jack at a time. 

The secondary of the OT is just wire wound around the iron core lams. Lets say, and this is not the true number, but, they wound 10 winds around the core and without cutting it they just cleaned the enamel insulation off of that wire and soldered in a wire fly lead, ie a tap, for the 8 ohm load, then they wound another 10 turns and soldered a fly lead to the winds end as the 16 ohm lead load.

So it's 1 continuous wire that is 'tapped' at a certain point. If you have 2 jacks hooked up to the 2 different ohm leads and you ground either 1 the whole wind is being grounded because the secondary wind is 1 wire. Ground the secondary, no signal goes to the speaker.

I’ll prolly go the single jack route as I only have I cabinet anyways.

Just for my own understanding :

Grounding all the ot taps with shorted jacks = bad

Open ot taps with no load = bad

Using a switch taps are open circuit however a load is connected so= ok

Using a single jack eliminates all this worry and thinking since I only have one cabinet and will re wire the speakers and set up the other output jack impedeance if need be.

Running only a 8 ohm jack  , will the NFB loop be ok, does the resistor need to change.

Hell since the forum is fruitful today, what exactly does a negative feed back loop do

[Willabe]

Do a search and read up on it;

What Does This Thing Do? — Negative Feedback Loop

i=d1m1RRggO5K7f7vm

i=YY-Y9G78-4XU-pp2

i=f1VRHzp4kDbNkkaa

[Snake5150]

Do a search and read up on it;

What Does This Thing Do? — Negative Feedback Loop

i=d1m1RRggO5K7f7vm

i=YY-Y9G78-4XU-pp2

i=f1VRHzp4kDbNkkaa

Thank you.

[mresistor]

So, tell us snake..  did you purchase an amp kit?  The layout you posted is from Triode Elect. but I don't assume you purchased their kit. 

[Snake5150]

So, tell us snake..  did you purchase an amp kit?  The layout you posted is from Triode Elect. but I don't assume you purchased their kit.

No I thought about a year ago it would be “cheaper” to source all the parts separately and go at it with literally no instructions. I’ve built alot of pedals and fix a lot of electronics. Took a long time and wasn’t cheaper. Live and learn.

As of now I am planning on a 4 input jtm45 with el 34s. Tube rectifier. Mallory 150’s and jj caps. I used 18g wire through the build.
The  transformers I got are pacific audio magnetics. The board is built and matches the layout. I’m just trying to get the power section sorted out.

I’m planning on using the Hoffman ground layout , and another person on here mentioned putting the cap before
standby switch. The transformer only has 8 / 16 ohm out which made me want to dual jack the outputs. Which is really a non issue since it’s just for me and I’m the only one that will use it. I’m pretty confident that I’ve done things correctly however am shy to post pics of the build on here to find out I screwed everything up. I’ll probably swallow my pride and do that however.

I literally built my own board, installed turrets populated the board. Got a blank chassis drilled it , mounted all the parts and am at the point we’re im just trying to check all the power section and tube stuff before I install the board and begin to think about firing it up.

If anyone has any resources from triode I’d be interested to look at them.


If anything looks totally teribble let me know. I know the lead dress could be cleaner but I think for the most part things are correct. I still need to deal with the output jacks, and need to clean everything up with a brush and some ipa.

Link to pics

https://imgur.com/a/u775MXp

[AlNewman]

One thing I see, is there could be a problem with cold joints or parts that seem to be tack soldered. 
It's like you are maybe not getting enough heat to your joints, or perhaps aren't keeping the tip of your iron clean and tinned.  I'm not sure what you're using for an iron, but even a 33W weller pencil iron should allow you to get the job done using proper soldering practices.
Watch a few videos on proper techniques and maintenance.  Soldering should be quick and easy, and it should all flow across all parts being soldered. 
Also, tack solders aren't ideal, it's normally best to put the wire through the eyelets and at least give them a half wrap for a structural bond.  Tools are also important, ideally you'd have a solder sucker, a good pair of tweezers, good lead based solder, etc.
That's besides the layout, it doesn't matter what your layout is if you don't have good solder joints.

[mresistor]

Thanks snake..   did you get the red series Pacific trans?  You're right sourcing the parts yourself is more expensive especially considering shipping from different companies.


The information gives us a better perspective of where you currently are in your build.

[Snake5150]

One thing I see, is there could be a problem with cold joints or parts that seem to be tack soldered. 
It's like you are maybe not getting enough heat to your joints, or perhaps aren't keeping the tip of your iron clean and tinned.  I'm not sure what you're using for an iron, but even a 33W weller pencil iron should allow you to get the job done using proper soldering practices.
Watch a few videos on proper techniques and maintenance.  Soldering should be quick and easy, and it should all flow across all parts being soldered. 
Also, tack solders aren't ideal, it's normally best to put the wire through the eyelets and at least give them a half wrap for a structural bond.  Tools are also important, ideally you'd have a solder sucker, a good pair of tweezers, good lead based solder, etc.
That's besides the layout, it doesn't matter what your layout is if you don't have good solder joints.

Some of them deff need to be re heated and re flowed. A lot of the connection have been soldered and re soldered I’ll clean them all up once things are settled with the design. The perks of a being a rookie with no instructions

[Snake5150]

Thanks snake..   did you get the red series Pacific trans?  You're right sourcing the parts yourself is more expensive especially considering shipping from different companies.


The information gives us a better perspective of where you currently are in your build.

Yes I got the red series pt,ot and choke. It’s a 45w transformer so not at all a true jtm 50 like like layout but accurate clone work is unimportant at this point. Just going for a working amp.