Into the rabbit hole...36 Watt EL34 Superlite TMB

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Billy_Goat
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Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Starting a build of a 36 Watt EL34 Superlite TMB! After my previous 18w build (not a 18watt.com build) and all of the frustration of that build, I'm hoping I won't have too many questions and all goes smooth with this build.

I do have one question to start though... Is there a technical reason why the tubes are identified (numbered) on the JMPGuitars 36 Watt EL34 Superlite TMB schematic as they are? The schematic shows V1, V3, V4, and two tubes identified as V5. (one of the EL34's and the other, the GZ34). There's no V2. Not a big deal, just something I noticed.

So with the above in mind... here's a photo of my turret board as it stands at the moment... I'll upload photo as things progress just for the fun of it or in case anyone wants to offer up comments that may be appropriate.

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Yes. The technical reason is that nobody told me that I didn't fix the labels. ;)

I updated it if you download the latest schematic. Let me know if you find any other mistakes.

Thanks,
Josh
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

That’s a sexy board, dude.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

ViperDoc wrote:
Sat 01/16/21 10:57 pm
That’s a sexy board, dude.
Yeah it is. I like how his turrets worked out for the ground bus.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

JMPGuitars wrote:
Sat 01/16/21 10:50 pm
Yes. The technical reason is that nobody told me that I didn't fix the labels. ;)

I updated it if you download the latest schematic. Let me know if you find any other mistakes.

Thanks,
Josh
Hey Josh,

Thanks for the schematic update!

I do have a question regarding the FX IN/OUT circuit... The schematic shows the input/output grounds as I would expect but the layout doc doesn't show the grounds being connected to the chassis or other grounding spots? ( See attachment ) Am I mis-reading the layout? Assuming the layout is not showing the ground connection and assuming it's a requirement, where would be the best place to connect the ground for the FX IN/OUT? At the input ground terminal?

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Billy_Goat wrote:
Sun 01/17/21 12:54 pm
I do have a question regarding the FX IN/OUT circuit... The schematic shows the input/output grounds as I would expect but the layout doc doesn't show the grounds being connected to the chassis or other grounding spots? ( See attachment ) Am I mis-reading the layout? Assuming the layout is not showing the ground connection and assuming it's a requirement, where would be the best place to connect the ground for the FX IN/OUT? At the input ground terminal?
Your assumption is correct that I assume people will read the schematic and know they need to ground the grounds on the FX loop.

Now....regarding where to ground. In theory it might be best to ground by the input jack as you stated. However, I have the jacks right near to the speaker jacks on my builds, and just run a ground through all the jacks. Maybe in theory this isn't great, but I haven't had any issues. The other thing to consider is that running a ground wire all the way across the amp isn't a great idea either. So experiment and see what works for you. Keep in mind that the FX loop is a potential point for issues including oscillations if you don't arrange things well.

Thanks,
Josh
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

JMPGuitars wrote:
Sun 01/17/21 8:47 am
ViperDoc wrote:
Sat 01/16/21 10:57 pm
That’s a sexy board, dude.
Yeah it is. I like how his turrets worked out for the ground bus.
Thanks guys... being in lockdown because of COVID leaves one with a lot of time to kick things up a bit - especially when waiting for parts to be delivered. While obviously not necessary to print a layout on a turret board as I did here, I like to spend time trying to undertand the circuits ( schematic , layout docs, and my actual build ) I'm working on and having an easy means to cross-reference my builds makes my head scratching go a lot less frustrating. Adding parts identification to the schematic, which I did, and then having the same identified on the turret board makes things easier to identify parts in the real world. Also, helps with my cross-referencing against my BOM doc.

Does it matter at all whether or not the on board wiring is on top of the board or underneath? I'm always concerned about having easy ( easier? ) access to all parts in case of problems. While it's "just a wire" and admittedly unlikely to be an issue either way, once the build is completed getting access to wires running under a board like this seems like a big headache task.

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Billy_Goat wrote:
Sun 01/17/21 1:14 pm
Does it matter at all whether or not the on board wiring is on top of the board or underneath? I'm always concerned about having easy ( easier? ) access to all parts in case of problems. While it's "just a wire" and admittedly unlikely to be an issue either way, once the build is completed getting access to wires running under a board like this seems like a big headache task.
On top of the board is better. Any time a thing goes under the board in my docs, it's because I don't want the thing making it harder to read the doc.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

JMPGuitars wrote:
Sun 01/17/21 1:11 pm
Billy_Goat wrote:
Sun 01/17/21 12:54 pm
I do have a question regarding the FX IN/OUT circuit... The schematic shows the input/output grounds as I would expect but the layout doc doesn't show the grounds being connected to the chassis or other grounding spots? ( See attachment ) Am I mis-reading the layout? Assuming the layout is not showing the ground connection and assuming it's a requirement, where would be the best place to connect the ground for the FX IN/OUT? At the input ground terminal?
Your assumption is correct that I assume people will read the schematic and know they need to ground the grounds on the FX loop.

Now....regarding where to ground. In theory it might be best to ground by the input jack as you stated. However, I have the jacks right near to the speaker jacks on my builds, and just run a ground through all the jacks. Maybe in theory this isn't great, but I haven't had any issues. The other thing to consider is that running a ground wire all the way across the amp isn't a great idea either. So experiment and see what works for you. Keep in mind that the FX loop is a potential point for issues including oscillations if you don't arrange things well.

Thanks,
Josh
Josh,

Yeah, I was wondering about the placement of the FX jacks. The layout doc seems to imply that they are to be placed on the control panel, but I want / need to place these jacks on the back panel.

When you say these jacks/ circuit have the potential for oscillations, what would be your best practice recommendation for the circuit installation? Put the caps and resisters as close as possible to the jacks and run shield wire to the board or ?? Atm, I'm planning on placing the jacks between the two preamp tubes and the two power tubes as my chassis is a GDS JTM45 offering that has three x 9 pin tube holes cut. Since I only need two x 9 pin tube holes for this build, I have the open space of a full 9 pin tube space to work with here.

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Billy_Goat wrote:
Sun 01/17/21 4:15 pm
Yeah, I was wondering about the placement of the FX jacks. The layout doc seems to imply that they are to be placed on the control panel, but I want / need to place these jacks on the back panel.

When you say these jacks/ circuit have the potential for oscillations, what would be your best practice recommendation for the circuit installation? Put the caps and resisters as close as possible to the jacks and run shield wire to the board or ?? Atm, I'm planning on placing the jacks between the two preamp tubes and the two power tubes as my chassis is a GDS JTM45 offering that has three x 9 pin tube holes cut. Since I only need two x 9 pin tube holes for this build, I have the open space of a full 9 pin tube space to work with here.
Nothing was intentionally implied with the placement on the layout, 'twas a matter of available space to show the jacks on the page. It can be placed on the front or back of the chassis.

This post has a photo of a recent build / how I do it: viewtopic.php?p=247480#p247480

Most of the time some minor chopsticking takes care of any issues. Shielded wire can certainly help.

Thanks,
Josh
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Reluctantly posting this as I have a feeling this should be noob obvious...

I'm making good progress on this build, but when I buzz out the in progress build / wiring for continuity issues at the input jacks ( opted to use the second optional jack ) just to be sure all is well going as I'm going along, I have continuity to ground no matter which jack lug I check on the input jacks. The same is true if I insert a 1/4" TS plug into either input jack. This seems strange as I would expect that at least with a TS plug in either of the inputs there would be an open circuit? Is this sort of continuity to ground expected, or indicative of a wiring issue on my part?

To be clear, I have the input jacks wired including the connection to ground as indicated in the build doc and the input jack tips wired to the the two 10k V1 resistors. The main board has not yet been installed / wired. Meter is connected to chasis ground lug and the the other lead used to check continuity at the jack lugs and at the terminal strip before V1.

I've checked the wiring against the build layout and the schematic multiple times and my build all seems as it should be.

Thanks in advance for any thoughts!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

To be safe, I highlighter verified the docs again, and the input as drawn is correct. Try looking at the schematic to understand what's going on better. Look very close at what is and is not connected in the drawing.

Post some good photos of your jacks so we can see what you have going on.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

JMPGuitars wrote:
Wed 02/03/21 5:52 pm
To be safe, I highlighter verified the docs again, and the input as drawn is correct. Try looking at the schematic to understand what's going on better. Look very close at what is and is not connected in the drawing.

Post some good photos of your jacks so we can see what you have going on.
Thanks, Josh. I wasn't thinking at all that your documents were in question, but appreciate your double checking.

So... my read here is that what I'm seeing is incorrect. I'll re-group and try to figure out what is going myself before seeking for more help and / or forwarding photos. I want to completely understand this for myself as a first choice goal.

I do have one question... The schematic shows the 'HI' jack in black. I'm assuming the the grayed out jack is the OPTIONAL jack referenced in your layout doc? Am I understanding this correctly?

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Billy_Goat wrote:
Fri 02/05/21 11:12 am
So... my read here is that what I'm seeing is incorrect. I'll re-group and try to figure out what is going myself before seeking for more help and / or forwarding photos. I want to completely understand this for myself as a first choice goal.

I do have one question... The schematic shows the 'HI' jack in black. I'm assuming the the grayed out jack is the OPTIONAL jack referenced in your layout doc? Am I understanding this correctly?

Cheers!
Do a highlighter test, and use the schematic also. It's honestly a confusing wiring, but it works if it's done correctly. Make sure only the one jack has the two side lugs connected to each other.

Correct, the grayed out jack is the optional one.
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

JMPGuitars wrote:
Fri 02/05/21 1:59 pm
Billy_Goat wrote:
Fri 02/05/21 11:12 am
So... my read here is that what I'm seeing is incorrect. I'll re-group and try to figure out what is going myself before seeking for more help and / or forwarding photos. I want to completely understand this for myself as a first choice goal.

I do have one question... The schematic shows the 'HI' jack in black. I'm assuming the the grayed out jack is the OPTIONAL jack referenced in your layout doc? Am I understanding this correctly?

Cheers!
Do a highlighter test, and use the schematic also. It's honestly a confusing wiring, but it works if it's done correctly. Make sure only the one jack has the two side lugs connected to each other.

Correct, the grayed out jack is the optional one.
Well, I think I've resolved this here... After checking and checking and checking and checking again, I couldn't see or find anything wrong with my wiring of the jacks. So, with this in mind I thought my only hope was to start removing the wiring and re-wire again hoping I'd find something amiss.

I started by removing the two shielded wires connecting to V1 pin 2 from the tips of the jacks. After removing these two connections, things seemed to test as I would expect. So... with that in mind, I wired up two new shield cables and the tested again. Seems to be as expected now.

Not sure what what was going on with the shielded cables in the first place as there doesn't seem to be any issues with the wire specifically after being removed from the build, but maybe there was a tiny wire shorting to ground that wasn't obvious? Sigh...

Onward and upward...

Cheers,
Greg
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Powered up my build today following Rob Robinette's DIY startup procedures.

All was going well until I added in the two V1 & V2 12AX7's at which time I detected the faint smell of something getting ready to smoke. All readings on my AC current and voltage meters were looking ok, but I visually could see ( and smell ) that the 1.5k 5W resistor between the two 50uF can caps was blackening to the point where the resistor code bands made the resistor appear like it was a 10R resistor instead of the required 1.5k resistor that I'm sure I wired in. My thermal temperature reader was showing this resistor sitting a bit under 200F.

So, I powered down, and removed the burnt resistor - which incidentally still read 1.5k - and replaced with a new 1.5k 5W resistor. Not seeing anything amiss after repeated previous highlighter run throughs and again another now, I crossed my fingers and tried again.

After an hour, all seemed well and the resistor was reading about 80F. Not sure what was going here, but...

Anyway, after adding in the power tubes, I let the amp cook for another hour and then pulled the tests voltage attached here. Everything seems to check out with a few over & unders by 10%-ish or less. ( Josh, I'm aware you have another thread in this forum where you want folks to post their voltage readings for this build which I will do when the build is completed.... ).

Please let me know if anyone sees any issues that I need to address here regarding voltages.

Didn't have time to move on to audio / signal testing, so that's next up... fingers crossed...

I do have one question... are there any particular tests / measurements I should make to confirm the correct operation of the FX send & return section other than simply plugging in a pedal or two and testing that way?

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

Followup up to the above...

After running the amp with both signal and guitar, all seems well with the exception of the FX circuit.

Volume is bold, loud and clear. Gain control working. Fat / Bright switch working as I would expect. All tone controls working. Amp sounds amazing!

As for the FX circuit... if I plug a straight guitar cable ( no pedals or effects ) between the send and receive jacks, there's no affect on the amp in general. When plugging in a pedal ( tried a delay and then tried a reverb pedal ), there's a horrid high frequency screaming noise (oscillation?). Inadequate shielding?

So, I'll go back and recheck the connections for the FX circuit, but any input anyone could add here for how to troubleshoot would be appreciated. Josh previously indicated earlier in this thread that this part of the circuit can be prone to stability issues, so maybe even a re-think of how I now have this area wired / shielded?

Thanks in advance!

Cheers!
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by JMPGuitars »

Your voltages look great! I'm looking forward to hearing a sample of your amp.

Post some photos of your FX loop from a couple different angles so we can see what's going on. The solution could be as simple as chopsticking the leads to avoid the oscillation.

Thanks,
Josh
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by ViperDoc »

Did you go with the 36 watt GDS transformer set on these amps or another make?
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Re: Into the rabbit hole...36 Watt EL34 Superlite TMB

Post by Billy_Goat »

ViperDoc wrote:
Tue 02/16/21 11:51 pm
Did you go with the 36 watt GDS transformer set on these amps or another make?
Yes, along with a GDS JTM chassis that I retrofitted for this build.

Cheers!
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