[Blueimac]

First Tube Amplifier build but after deciding on the "Jonokuchi" destop amp as a first build I haven't been able to find any recent updates form other builders, I have some questions to be answered and hopefully will find some help here - I'm looking forward to getting the PCB soon so I can get started. 
 
 
 
 
 
First question is about the #6-32 x 1/4" standoffs for supporting the PCB, Should the standoffs be metal (which I'm assuming would ground the PCB to the chassis) or Nylon to prevent grounding the PCB ?
 
 
Second - Would a pair of Sylvania GE 6EM7 tubes be a suitable replacement for the 13EM7 13v filament tubes ? I haven't been able to find many 13EM7 tubes and was wondering if there are any tubes that could be used as replacements ?
 
 
Any input on better quality replacements for C5 and C6 - 0.1uF 630V coupling capacitors ? I've been looking at the Obbligato Gold Premium Capacitors 
 
 
Last - I'm thinking about a minimalist chassis design with a cleaner look, Would it be possible to conceal the three transformers inside the chassis if kept away or shielded from the PCB ?
 
 
 
 
Also for anyone who may be building this project soon here's one update for now on the Jonokuchi BOM as this part is no longer available from Mouser -
 
 
D1 - Fairchild Bridge rectifier 2A 50V - 3N253  (Mouser Part # 512-3N253) is no longer available so I'm using the following in it's place 
 

Mouser Part #:	625-2KBP005M-E4
Manufacturer Part #:	2KBP005M-E4/45
Manufacturer:	Vishay Semiconductors
Description:	Bridge Rectifiers 2.0 Amp 50 Volt

 
 
 
 
 

 

 

[Blueimac]

First Tube Amplifier build but after deciding on the "Jonokuchi" destop amp as a first build I haven't been able to find any recent updates from other builders, I have some questions to be answered and hopefully will find some help here - I'm looking forward to getting the PCB soon so I can get started. 
 
 
 
 
 
First question is about the #6-32 x 1/4" standoffs for supporting the PCB, Should the standoffs be metal (which I'm assuming would ground the PCB to the chassis) or Nylon to prevent grounding the PCB ?
 
 
Second - Would a pair of Sylvania GE 6EM7 tubes be a suitable replacement for the 13EM7 13v filament tubes ? I haven't been able to find many 13EM7 tubes and was wondering if there are any tubes that could be used as replacements ?
 
 
Any input on better quality replacements for C5 and C6 - 0.1uF 630V coupling capacitors ? I've been looking at the Obbligato Gold Premium Capacitors 
 
 
Last - I'm thinking about a minimalist chassis design with a cleaner look, Would it be possible to conceal the three transformers inside the chassis if kept away or shielded from the PCB ?
 
 
 
 
Also for anyone who may be building this project soon here's two updates for now on the Jonokuchi BOM as these parts are no longer available from Mouser - 
 
 
C1,C2 - 1uF 100V film cap 5mm LS  Wima (Mouser Part# 505-MKS21/100/10) using the following in it's place 
 
VISHAY-RODERSTEIN
[size=1.2em] MKP-1837 Metalized Polypropylene[/size]
[size=1.2em] Film Capacitor[/size]
[size=1.2em]  [/size]
[size=1.2em] http://www.partsconnexion.com/capacitor_film_visrod.html#14846[/size]
 
 
D1 - Fairchild Bridge rectifier 2A 50V - 3N253  (Mouser Part # 512-3N253) using the following in it's place 
 

Mouser Part #:	625-2KBP005M-E4
Manufacturer Part #:	2KBP005M-E4/45
Manufacturer:	Vishay Semiconductors
Description:	Bridge Rectifiers 2.0 Amp 50 Volt

 
 
 
 
 

 

 

 

[Greystoke]

I've got the PCB for this kit almost fully populated, waiting on tube sockets (got a couple of different styles to try) before cutting the top plate.  I've also left off the switches and jacks on the front edge, thinking of doing a slightly larger case so I'll need to adjust the spacing of the front controls.
 
I didn't realize until I started this post that this is kind of a necro-thread; anyone built one of these kits lately?

 

[tdubl07]

This build was a fun one. And requires patience since ordering the transformers took about 6-7 weeks for delivery. Well worth it. Lots of power, and sounds great. Anyone thinking about building one, go for it. Tubes are still readily available if you know where to look. Check antique radio supply or vacuumtubes.net

 

 

[vmvietnam]

So kool! Thanks for sharing yet another neat amp!

 

[guppysb]

Hey Guys,
 
Thank you Mr. Millett for creating such wonderful projects for us do to. Just bought all the parts, and I guess the transformers will arrive in 6-8 weeks. So excited, this is my first DIY project. I have a Computer Engineering degree, but nowhere close to that of a EE, so just a bit nervous about the high voltage. If you guys don't mind, I have a few questions:
 
1. What gauge of wiring should be used for the speaker binding posts to the PCB, along with the RCAs?
 
2. I see that HighFlying9 added a power light to the project. If I wished to add an LED, perhaps with an inline resistor to ground, where should I connect LED in terms of power to? It's been a while since I did some EE, software engineering is a bit easier, hehe. Using this as a reference: http://electronics.stackexchange.com/questions/32965/add-on-off-indicator-led-to-circuit
 
Please let me know if there is an easier solution.
 
3. It looks like both the 1/4" and 1/8" jacks can be placed on the board. I have the Sennheiser HD 650 and a BeyerDynamic DT 990 250 ohm. That's a combined impedance of roughly 550 ohms. Would the amp be able to drive both sets of headphones at once, one placed on the 1/4" and another on the 1/8"? 
 
4. I also have a set of Behringer Audio Truth 3030A (active studio near field monitors), which I connect using a direct input box (input is RCA, output is balanced XLRs to the speakers). Will I have any issues if I use the output of the 1/4" or the 1/8" to RCA to send the signal to the direct input box? Just curious as to your take on it.
 
5. I've been doing a lot of reading at: http://www.diyaudio.com/forums/tubes-valves/182269-jonokuchi-new-desktop-amp-little-red-board.html
It seems that spacing the OPTs by 2 or more inches away from each other helps the hum. I am thinking of going with acrylic as an enclosure, instead of a metal one. Will I have issues with the POT humming with acrylic, or any other issues?
 
Sorry if I have really dumb questions, just trying to learn a bit. Thanks for the help. 

 

[zeroecco]

Built one of these myself,
 
I have to say that on my beyer T70's this amp struggles a bit. I have to run at close to full tilt to get the volume these headphones need.

 

[guppysb]

Hey Guys, Finally finished putting the amp together this weekend, after all the parts arrived. I am, however, having some issues. I would appreciate any suggestions for debugging the following issue: I have very little sound output from the left channel. It does not matter if I use 1/8" front or the rca rear inputs. It also does not matter if I use the 1/8" or the 1/4" outputs. Perhaps a bad ground? Also, when I slightly move the amp or the pot, I get static on the left channel as well. With a little bit of moving the amp, the static goes away. Everything seems to be left channel related. I don't have passive speakers to test the speakers output, so this is strictly a headphone out issue so far. Please let me know what I can debug, would greatly appreciate any help.

 

[Mr Rick]

  Hey Guys, Finally finished putting the amp together this weekend, after all the parts arrived. I am, however, having some issues. I would appreciate any suggestions for debugging the following issue: I have very little sound output from the left channel. It does not matter if I use 1/8" front or the rca rear inputs. It also does not matter if I use the 1/8" or the 1/4" outputs. Perhaps a bad ground? Also, when I slightly move the amp or the pot, I get static on the left channel as well. With a little bit of moving the amp, the static goes away. Everything seems to be left channel related. I don't have passive speakers to test the speakers output, so this is strictly a headphone out issue so far. Please let me know what I can debug, would greatly appreciate any help.

I would start by swapping the tubes around. If the problem stays on the left channel I would start looking for cold soldered joints or loose connections.

 

[guppysb]

Quote:

  I would start by swapping the tubes around. If the problem stays on the left channel I would start looking for cold soldered joints or loose connections.

Thanks for the reply Rick!
 
I had swapped the tubes and it didn't make a difference. I originally thought the issue was with my 1/8" output jack and so I de-soldered it and replaced it with a new one. Now, not only do I have the same issues as before (can't really hear left channel), there is also a loud buzzing on the right channel. The buzzing gets louder as I increase the volume. I inspected all the solder joints to make sure there was enough solder and there weren't any solder bridges. Checked for continuity with my DMM. I guess I'll just try to resolder the shifty looking joints tomorrow.

 

[wotts]

As for the buzzing, did you install the jack with the updated instructions on Pete's website? I think there are resistors added to the rear legs of the jack. I'd have to look to be sure.
 
I would reflow the solder joints just to be sure for the channel issue. Might be something faulty driving the tube. It's been a while but I recall transistors inside...did one get too much heat on install?

 

[Mr Rick]

  Quote:
Thanks for the reply Rick!
 
I had swapped the tubes and it didn't make a difference. I originally thought the issue was with my 1/8" output jack and so I de-soldered it and replaced it with a new one. Now, not only do I have the same issues as before (can't really hear left channel), there is also a loud buzzing on the right channel. The buzzing gets louder as I increase the volume. I inspected all the solder joints to make sure there was enough solder and there weren't any solder bridges. Checked for continuity with my DMM. I guess I'll just try to resolder the shifty looking joints tomorrow.

Yes, take a break. Tomorrow the problem might just jump out at you. It's worked for me.

 

[guppysb]

Quote:

  As for the buzzing, did you install the jack with the updated instructions on Pete's website? I think there are resistors added to the rear legs of the jack. I'd have to look to be sure.
 
I would reflow the solder joints just to be sure for the channel issue. Might be something faulty driving the tube. It's been a while but I recall transistors inside...did one get too much heat on install?

Hey Wotts,
 
I didn't do the resistor mod described on Pete's website. I ordered a chassis 4 inches wider than the one he used, and spaced apart the output transformers from the main power transformer. I could try to do the mod tomorrow and see where it gets me. I wonder if I can remove the 2 10 ohm resistors from R22 and R23 and use it for the mod. Although, he mentioned that 220 ohms was used in the mod.

 

[wotts]

The other thing that comes to mind is a ground loop. I'll have to crack mine open and take a look. Or maybe I have pictures...I'll look and get back to you.

 

[guppysb]

Thanks Wotts! I have a hammond aluminum chassis. I know one of the pcb mounting holes is meant to be grounded. I have my pcb mounted to the chassis with washers and bolts on all the mounting holes. Doing a continuity test, all the mounting holes go back to ac ground.
What is worrysome is that the 1/4" also has quite a few ground connections, along with the 1/8" jacks, and also the switches. I know this is going to sound stupid, but was I not supposed to solder all the holes for the switches/jacks/pot? I assumed I was since it looked like Pete made it so a standard item could fit in there.
 
I guess tomorrow will be filled with soldering/desoldering/looking at the schematic to see where I went wrong. I'll post some pics of my PCB tomorrow and maybe you guys can point out where I messed up. Thanks again for the replies guys, good to know I am not alone here and out $350.