It's BUILD Time!

[Shannon Parks]

I just realized that I never did this! OOPS!

I looked the 12AX7 and 6SL7 up with TDSL, thinking I could sort this one out without a problem...alas...

It visually appears that the traces connect like this (12AX7 to 6SL7):

And getting here would take more than just two jumpers...

HELP!...

Thanks (as always) guys,
drew*

Hi drew*,

Just so I don't confuse myself, just switch the jumpers the other way and you'll be fine.

Just think about the board and the 6SL7 as I connected the 6SL7 to the PCB manually in layout and didn't piggyback it onto the 12AX7:

1 - Grid 1 - Floating
2 - Plate 1 - Floating
3 - Cathode 1 - Floating
4 - Grid 2 - Connects to jumper Z
5 - Plate 2 - Connects to jumper Y
6 - Cathode 2 - Shares same cathode circuit as the 12AX7 (pin 8)
7 - Heater - 6.3VAC A (shares with the 12AX7 circuit)
8 - Heater - 6.3VAC B (shares with the 12AX7 circuit)

Shannon

[nineno]

Just so I don't confuse myself, just switch the jumpers the other way and you'll be fine.

Thanks Shannon. I took your advice and just hooked the wires up.

Luckily, I had never hooked the jumpers up before, so I didn't need to un-do anything. I have another question though, regarding the manual.

I had an eariler revision of the manual than the one that is currently posted on the website, and a Rev. B board.

The step 9 in my istruction manual is "Solder Rx47 in series with Cx20 in a teepee fashion from V2-4 to the ground of R11. This is a low pass filer ensuring stability."

The revised manual on the website doesn't have this step. Step 9 is the set regarding the jumpers, and step 10 is the same step 10 that my manual has. I have installed the Rx47 and Cx20 as stated...do I need to remove this?

I've taken a picture of itso you can see what I did. I used the footprint of C8 that is connected to V2-4 and the ground-side footprint of R11. See here:



Thanks, again!
drew*

[nineno]

Earlier today I picked up some NOS RCA 6SL7GTs from a guy in town. This was the last thing that I needed before firing up the amps for the first time.

I got home cleaned up some of the x-former/power wires and then followed through the Ohm-Out proceedure. Everything checked out OK.

I removed J4-8, and meaured the voltages. Everything seemed good, except J4-1 and J4-2. They're listed as 67V and 65V. I get 120V (which is what I expected, since that's the power inlet, right?)

I re-attached J4-8, stuck the tubes in, and plug the first unit in. After it had a few seconds to charge up it began squealing...it was the output transfromer end bell. By touching it, even lightly, I could damp out the noise.

I began trying to set the bias. TP1 dropped down to 0.550V pretty quickly. TP2 however, I couldn't get to go low enough. I assumed I had a resister stuffed wrong, so I turned my attention to the other amp. I figured if I could get that one dialed in then I could check the non-compliant one verses a working one.

However, I had the EXACT same results with the second amp. This time, though, I left the amp plugged in longer and the squealing stopped after about 5 minutes, but then I couldn't set the bias at all. Both TP1 and TP2 were registering zero. As I probed around the board, checing voltages the squealing came back suddenly. I think It was when I touched the probe to pin 6 of the 6SN7...?

I had the Rx48 and Cx21 in series on the 8Ohm outputs of the x-former, nothing at all on the input (not even wires).

Also, did Rx47 turn into R49and Cx20 turn into C8 in a manual revision? It appears that is the case, but I'd like that verified.


Help!!
drew*

[Shannon Parks]

... I have another question though, regarding the manual.

I had an eariler revision of the manual than the one that is currently posted on the website, and a Rev. B board.

The step 9 in my istruction manual is "Solder Rx47 in series with Cx20 in a teepee fashion from V2-4 to the ground of R11. This is a low pass filer ensuring stability."

The revised manual on the website doesn't have this step. Step 9 is the set regarding the jumpers, and step 10 is the same step 10 that my manual has. I have installed the Rx47 and Cx20 as stated...do I need to remove this?

Hi drew*,

This threw me for a second - I missed this original post. The Rev A needed that 'teepee' low pass filter added as Rx47 and Cx20 (due to no PCB footprint). The Rev B has this filter located at C8 and R49. Looking at your Rev B board, it looks OK the way you have it set up - same difference. It is omitted in the latest manual since the parts are added from the parts list.

Shannon

[Shannon Parks]

Hi drew*,

BTW, sorry for the slow reply as I was visiting the Skyline chili capital this past weekend.

I removed J4-8, and meaured the voltages. Everything seemed good, except J4-1 and J4-2. They're listed as 67V and 65V. I get 120V (which is what I expected, since that's the power inlet, right?)

I dunno what I had planned there - I must've measured the AC referenced to the chassis? But you are correct.

I began trying to set the bias. TP1 dropped down to 0.550V pretty quickly. TP2 however, I couldn't get to go low enough. I assumed I had a resister stuffed wrong, so I turned my attention to the other amp. I figured if I could get that one dialed in then I could check the non-compliant one verses a working one.

However, I had the EXACT same results with the second amp. This time, though, I left the amp plugged in longer and the squealing stopped after about 5 minutes, but then I couldn't set the bias at all. Both TP1 and TP2 were registering zero. As I probed around the board, checing voltages the squealing came back suddenly. I think It was when I touched the probe to pin 6 of the 6SN7...?

Sounds like your basic oscillation...

I had the Rx48 and Cx21 in series on the 8Ohm outputs of the x-former, nothing at all on the input (not even wires).

This probably the problem - short the input for now. Also, it may not be a bad idea to disconnect the NFB for now, too. You won't have to re-bias when hooking it back up.

Also, did Rx47 turn into R49and Cx20 turn into C8 in a manual revision? It appears that is the case, but I'd like that verified.

Correct.

Go ahead and:

- remove the NFB
- short the input
- jumper the chassis temporarily to the PCB
- double check that your output tranny is ground referenced to the PCB at J4-3
- try again (shut down if oscillation re-occurs) and report back

Good luck!

Shannon

[nineno]

Hi drew*,

BTW, sorry for the slow reply as I was visiting the Skyline chili capital this past weekend.
...
Sounds like your basic oscillation...
...
Go ahead and:

- remove the NFB
- short the input
- jumper the chassis temporarily to the PCB
- double check that your output tranny is ground referenced to the PCB at J4-3
- try again (shut down if oscillation re-occurs) and report back

Skyline Chili Capital? Sounds interesting...What is it?

Thanks for the help. I'm currently at the SAE Noise and Vibration conference in Traverse City, MI, but I'll get back to the amp hopefully no later than Sunda afternoon and have it all sorted out by then.

I'll let you know how it pans out...
drew*

[Shannon Parks]

Skyline Chili Capital? Sounds interesting...What is it?

Cincinnati (aka the Queen City aka Cincitucky). Here's an interesting piece of Cincy forgotten history:
http://www.forgottenoh.com/subway.html

I'm currently at the SAE Noise and Vibration conference in Traverse City, MI...

http://www.sae.org/events/nvc/
http://www.sae.org/events/nvc/ataglance.pdf

Maybe you can give us some sound deadening tips later on. I think I might sound proof the lab this summer for those late night 'tests'.

Shannon

[nineno]

Sounds like your basic oscillation...
...
Go ahead and:

- remove the NFB
- short the input
- jumper the chassis temporarily to the PCB
- double check that your output tranny is ground referenced to the PCB at J4-3
- try again (shut down if oscillation re-occurs) and report back

...but I'll get back to the amp hopefully no later than Sunda afternoon and have it all sorted out by then.

I'll let you know how it pans out...

OK, I'm another step closer.

Shorting the input jumper seems to have taken care of the oscillation as long as the jumper or an input device (CD player) is hooked up. As soon as the jump or input is disconnected I'm right back to oscillation and/or hum. I know this shouldn't ever really be a problem, but if I turn the amp on without anything connected (to verify/reset the bias, for example) this will always happen, right? Is this expected behavior? Is there something I can change to prevent this behavior?

I also relocated the input shield to the same terminal as the transformer ground. Unfortunately there was still some hum in the speaker after doing this. I think this is because of the way that I have line/B+/output transformer wires routed, or perhaps the chokes orientation.

I'll finish building the chassis and then change the wiring and choke location to try to fix this.

One last thing: I'm running 6CA7 power tubes. Do I need to change the bias setting from 550mV?

Thanks
drew*

[Shannon Parks]

Shorting the input jumper seems to have taken care of the oscillation as long as the jumper or an input device (CD player) is hooked up. As soon as the jump or input is disconnected I'm right back to oscillation and/or hum. I know this shouldn't ever really be a problem, but if I turn the amp on without anything connected (to verify/reset the bias, for example) this will always happen, right? Is this expected behavior? Is there something I can change to prevent this behavior?

Hi nineno,

Lowering V1's grid resistor (R2) to 100K from 470K should do the trick.

I also relocated the input shield to the same terminal as the transformer ground. Unfortunately there was still some hum in the speaker after doing this. I think this is because of the way that I have line/B+/output transformer wires routed, or perhaps the chokes orientation.

I'll finish building the chassis and then change the wiring and choke location to try to fix this.

Choke is probably fine. Send me a pic of wiring hookup after your are done and I'll take a look.

One last thing: I'm running 6CA7 power tubes. Do I need to change the bias setting from 550mV?

55mA is fine for these tubes. You might try 60mA (600mV) later. I personally love to run these tubes hard.

Shannon

[nineno]

OK, I still haven't finished the chassis for my Ikes, but I plugged them in again to explore the humm phenomena (mentioned above).

The 60Hz humm came, as I expected, so i began snipping the wire-ties that bundled the various wires together under the chassis. Nothing really seemed to help..and then I grabbed the metal panel that everything is mounted to near a transformer mounting screw and the humm reduced significantly.

The PBC is connected to the aluminum top panel by metal screws, so that should be grounded. The transformers are also attached to the same panel with screws. However, the x-formers could be semi-insulated b the paint on the transformers.

Regardless, what is anyone/everyone's philosophy on what appears to be a ground-plane problem?

Tomorrow I'm going to the furniture-grade wood store to find something to make a pair of chassis with...maybe I'll finish the amps this year...?

thanks, as always...
drew*

[Shannon Parks]

Regardless, what is anyone/everyone's philosophy on what appears to be a ground-plane problem?

Hi drew*,

Please send me a couple pictures if you can. Note that the Rev B Ike's standoffs are not connected to the PCB ground. The leakages in the transformer provides a DC reference through the HT center tap, I believe. You might tie a jumper from the J4-3 or J4-4 or J4-5 (experiment with all three - one might work better than the others) to the transformer lug where your safety ground is attached to the chassis. Also, disconnect your RCA input ground from J1-2 and connect it to J4-3 (if you haven't already).

Shannon

[nineno]

Please send me a couple pictures if you can.
...
You might tie a jumper from the J4-3 or J4-4 or J4-5 (experiment with all three - one might work better than the others) to the transformer lug where your safety ground is attached to the chassis.
...
Also, disconnect your RCA input ground from J1-2 and connect it to J4-3 (if you haven't already).

Shannon, thanks.

Here are some links to pictures.
A view of the PCB from above...
http://jupiter.walagata.com/w/nineno/ground_problem_003.jpg
A profile shot attempting to show stand-offs, x-former mounting, etc...not too useful, but sort-of a neat shot. haha...
http://jupiter.walagata.com/w/nineno/ground_problem_004.jpg
A slightly closer look at the bundle of wires...
http://jupiter.walagata.com/w/nineno/ground_problem_005.jpg

Incidentally, my safety ground currently runs from one of the ground-plane pins (3, 4, or 5) to the AC socket ground. Is that correct? I double checked the manual that I have, and that's what is shown.

I'll try directly grounding the x-formers this afternoon/evening. I have to run into the big city today, so I'll take the oppertunity to buy chassis-making material...you know something is wrong with the world when you have to drive into a million+ person metro area to buy fine lumber. (?!)

Also, as you can see, I hacked an input sheild to J4-3. Rest assured, that's not the final wiring technique, just something for now. Even when I directly snub the input to the input ground/shield the unit hums, so I don't think my hum is related to that incredibly poor interconnect.

Hope the pics tell you something. Let me know if you need a more specific shot.

drew*

[nineno]

Well, I've often suspected that I was getting less-smart as the months rolled by, but now there is proof...

I added a gound-strap to the metal top-panel of my amplifier and it did a tremendous job of cleaning up the humm that was being produced...

Of course, if you look closely at the pictures I've linked to in my last post you can see that I had the temporary input wire hooked up wrong...

The grounding of the top panel/x-former cleaned the sound up a bit with the input hooked up wrong. It fixed everyhting 100% when the input was hooked up properly...astonishing.

Of course, on the ST-35 I built nearly two years ago i was smart enough to ground the x-formers the FIRST TIME. I discovered that when I decided to check the bias of the Baby Blue, since I was tubing this afternoon.

I also did namage to get some wood for making both Ike chassis. I also got some "unique" wood stains, too. So I'm rather interested to see how these turn out.

drew*

[Shannon Parks]

I added a gound-strap to the metal top-panel of my amplifier and it did a tremendous job of cleaning up the humm that was being produced...

Of course, if you look closely at the pictures I've linked to in my last post you can see that I had the temporary input wire hooked up wrong...

The grounding of the top panel/x-former cleaned the sound up a bit with the input hooked up wrong. It fixed everyhting 100% when the input was hooked up properly...astonishing.

Great news! I'll make sure the manual gets edited to clearly explain the safety ground. In a nutshell, the safety ground and the power ground meet at a transformer lug, and star washers can ensure a good connection between the two and the chassis. Currently, the signal ground is directly connected to the power ground in the PCB ground plane. Luckily, connecting the output transformer ground and the signal input ground together at J4-3 does a pretty decent job.

I also did namage to get some wood for making both Ike chassis. I also got some "unique" wood stains, too. So I'm rather interested to see how these turn out.

Can't wait to see them!

Shannon

[nineno]

Well, it's been...*gasp*... three and a half months since I posted anything about my build, so I thought I'd at least post an update:

The build has completely and totally stalled out, and not at all for any technical reason. The major hang-up right now is finding the time/tools to make a chassis. Originally I had a co-worker that is an exceptionally talented wood worker that was going to donate his time, tools, and talent to helping me make some nice little chassis’s but he and I both started looking for new jobs. The good news is that we've both found new jobs, but at the expense of making any head-way with the amplifiers. Don't you just hate it when careers get in the way of hobbies?

However, like any good DIYer I've used this down time to re-think my entire build-up and invent even more features to add to the amp (ha-ha-ha). As a result, I thought I should seek some opinions here on weather or not these are ideas worth pursuing.

My idea is to build a central 'control box' for both amplifiers. This would be a purpose-built pre-amplifier for the Ikes. It would have at least one line input (multiple inputs is an option, too), volume control (active or passive...unsure which), and a power button. There would then be an umbilical cord to each amplifier from this pre-amp/control box.

The pre-amp would allow for a single, centralized location to plug in the source(s) and control the volume, but the power button on the pre-amp would also turn on the amplifiers. Therefore, the umbilical cord to the amplifiers would have a low-voltage analog signal for the music, and another low voltage pair (5 or 12VDC) to control power relays in the amplifiers.

There isn't a great technical reason for doing this, other than it might be sort-of 'cute.' It'd also allow me to remove extraneous circuitry from thee amplifier chassis: Originally I planned to have a tactile (push-on/push-off) button/LED indicator on the front of each amplifier. I could utilize this same circuit inside of the pre-amp box, but use only 1 of these circuits, not 2. If I did take this approach I'd probably use LEMO or Amphenol connectors from the pre-amp to the amps to reduce the number of connectors on the back. Then, the only other connectors that I'd need to have on the amplifier are mains input and speaker output (I planned on using Neutrik PowerCon and Speakon, respectively for those tasks). I could also put a little power indicator LED/etc on the front panel without any trouble.

So, feel free to make comments, suggestions, or just blow a hole through that idea. Hopefully I'll have a chance to make the chassis for the amps at least in the next few weeks/months...

drew*