It's BUILD Time!

[nineno]

Hey guys,

This forums has been pretty quiet for awhile so I thought I'd start asking some questions!

Here's the skinny:

I'm building a pair of Ikes. I've ordered most of the parts already and I'm in the process of ordering tubes which is where I'm hitting some stumbling blocks.

I want to use the 6CA7 big bottle ElectroHarmonix tubes, based on the glowing reviews here and on other sites.

If I use these tubes do I have to adjust the bias using R29, or does it remain the same (resistor value of 3.3K)? Do I have change anything major, like transformers?

I'd also like to use the 6SL7 pre-amp tubes, just for the look of the 4 octal tubes. I've noticed there aren't a lot of options for the 6SL7 from the normal 'retail' outlets (Uncle Neds, thetubestore.com, Angela), but there are some. Right now I'm thinking of using the United Electron (sylvania) on Angela or the Sovteks on thetubestore.com. Should I avoid the 6SL7 becasue of the limited selection or would one/both of these do just as good a job as the 12AX7? Any suggestions on which might be better if I do go with one type of the 6SL7s above?

That's the first round of questions that I have, but I'll have more as time goes by. Thanks in advance, guys!

drew*

[Shannon Parks]

Hi drew*,

I've been chatting with Thermion this week as he is planning an all octal Ike pair. Using the stock values you can plug a 6SL7 in there (just set the Y & Z jumpers the other direction). BTW, note the placement of the 'keys'.

I would guess that so much NOS stuff is out there, that there has been little need for the foreign factories to make any. But I would worry about it at all. You could even buy a small stash that would last you forever, if need be. Hey, building up a tube hoard is part of this hobby, right? 8^)

As far as the bias is concerned, no changes need to be made. The bias supply can down beyond -70VDC. The grid resistors are 100K, allowing use of any of the power tubes.

Shannon

[Thermion]

Drew,

I am currently collecting components for my Ike project. As Shannon said, I want to build an all octal pair. My experience with tubes has been that run of the mill old stock tubes perform and test far better than current production. I don't think the selection of 6SL7s is too bad. I have had good luck from Antique Electronic supply and other internet suppliers. Right now, US NOS 6SL7's and 6SU7's are selling for about $7.00 to $10.00 apiece. Go ahead and buy a few from 4 or 4 different sources and you will have a stash that will last longer than your amps will.

[TerrySmith]

As far as 6SL7's go, I've tried GE, Sylvania, and RCA black plates. The RCA's sound far better than the other two.

Just my $.02!

[Thermion]

Drew,

My previous post was submitted before I finished it. I have run some circuit simulations on the Ike circuit and want to share my thoughts to others who want an all octal amp. If you replace the 12ax7 with a 6sl7 and keep the same circuit values, everything should work fine. However it will not be exactly optimal. The 6sl7 will draw slightly more current (.92 ma versus .87 ma) which reduces the DC voltage going to the grid of the phase splitter (123v versus 128v). This voltage sets the operating point of the phase splitter and reduces the current there (7.2 versus 7.5). These are small changes, and you would probably never be able to hear it, but the octals like a little more current to sound their best. I recommend reducing R30 to give a B+ voltage of 250 volts versus 215 volts on the 6sl7. This gets more current going through the 6sl7 (1.09 ma) and sends a DC voltage of 141 volts to the phase splitter. This in turn will create an idle current of about 8.2 ma through the phase splitter and keep it happier. The good news is the only component change is R30.

I have decided to use a 6sn7 in place of the 12ax7. This will reduce the overall gain of the amp, but that may be desirable if you plan to use an active linestage. If using a passive linestage or a CD player with a volume control the 6sl7 is a better choice.

JT

[Guest]

Excellent information guys, thank you all.

Thermion, thanks for the detailed explaination of the tube opperating points for 12AX7 vs 6SL7. Given the information that you all provided I see no reason not to march ahead with the 6SL7-all octal amp.

I think I've decided to get the JAN Phillips 6SL7 that Angela sells for $10 each, to start with. I'll test others once I get Ike up and running.

Thermion, you mentioned changing R30 to compensate for the higher draw of the 6SL7. Would you mind explaining the calculations done to re-calculate R30? If it's more trouble than it's worth you can just tell me the new value of R30, but i wouldn't mind having the explaination of the relationship. I'm assuming it's a couple rounds of V=I*R, and I can certainly handle that.

Once Uncle Ned and the folks at Angela return from their respective vacations the big-dollar parts should be on their way.

Tomorrow I'm going to start laying out my chassis (actually, i started months ago, but something isn't just right yet...).

Thanks again, guys!
drew*

[Thermion]

Thermion, you mentioned changing R30 to compensate for the higher draw of the 6SL7. Would you mind explaining the calculations done to re-calculate R30? If it's more trouble than it's worth you can just tell me the new value of R30, but i wouldn't mind having the explaination of the relationship. I'm assuming it's a couple rounds of V=I*R, and I can certainly handle that. drew*

Yes it is a simple V=I*R calc. You have current through the 6sl7 and R43. My simple calcs show about 1.6 ma and a desired voltage drop of 195 volts. So replacing R30 with a 120K resistor will work. Tube circuits are relatively forgiving, so if you are within 5-10 volts that is OK. I suggest trying 120K and then seeing what voltages you get in the finished amp. You can always tweak R30 and R29 at that point to get what you want.

JT

[nineno]

Hey, just out of curiosity, approximately how many amps will one Ike amplifier draw when completed in stock fashion?

drew*

[Shannon Parks]

Hey, just out of curiosity, approximately how many amps will one Ike amplifier draw when completed in stock fashion?

drew*

It should be very close to the ST35 - around .8A at idle.

Shannon

[nineno]

Are there specific hole location/dimensions available for the Ike Rev B?

I saw the limited dimensioning in the manual, but that doesn’t call out where the holes are on the PC board.

Thx,
drew*

[Shannon Parks]

Are there specific hole location/dimensions available for the Ike Rev B?

I saw the limited dimensioning in the manual, but that doesn’t call out where the holes are on the PC board.

Thx,
drew*

Hi Drew,

Yes, that template isn't as useful as it should be. Here's some help docs:

Hole dims in a text file

PDF with small ref picture and the same dims

For more fun, you can go to Front Panel Expressand use their software to look at these files:

A template of the PCB dims only

A beta version of a 8" by 16" top plate
This is just me experimenting - I haven't ordered one yet. But I intend this one to use a Hammond 270HX and Hammond 1620. It'll be tube rectified 6B4 monoblocks.

I haven't used FPE, but I have heard good things from the guys over at AudioAsylum. I do believe their prices are less than last time I checked, as they now appear to have a sister shop in Washington state instead of everything in Europe. The software is amazingly good!

Shannon

[nineno]

Shannon, thanks for the hole location information. I'll check into the freeware design software later, too!

I have another, seemingly dumb, question: I've decided to use the C-354 Choke from Triode Electronics as suggested in the manual. I assumed this replaced R27 & R28 because of the comment "--alternatively use C-354 choke from Ned (recommended)."

However, when looking at the schematic on page 12 of the manual I see that both of the resistors and the choke are shown. So, do I need to run all three components in parallel?

Thanks again!
drew*

[Shannon Parks]

However, when looking at the schematic on page 12 of the manual I see that both of the resistors and the choke are shown. So, do I need to run all three components in parallel?

Thanks again!
drew*

No - just use one or the other. Trying to 'illuminate' the modifications on the main schematic can be a little difficult. I'll probably just end up having a repository of modded schematics on the website (eg like the Fender ST35, tube rectification, etc.).

Shannon

[nineno]

Well, the iKE build-up is going much slower than I had hoped, but it's progressing, none-the-less.

A couple months ago I actually soldered in most of the resistors and capacitors to the board, and three weeks ago I made my top-panels which allowed me to mount the sockets (I've found its much easier to solder the sockets in once the board is mounted to the chassis panel, with the socket centered in the through-hole).

However, it was no-easy task finding a 1.0625" panel punch designed to punch out 0.125" AL sheet stock, but in the end I got it taken care of. The holes around the octals aren't as clean as I would have liked, but they get covered up by the octal bases anyway. (see links below: BIG pictures)

http://jupiter.walagata.com/w/nineno/semi-assembled_001.jpg
http://jupiter.walagata.com/w/nineno/semi-assembled_004.jpg

In hind-sight, the aluminum panel might not be as optimal as a ferrous (iron/steel) top cover, but it looks pretty nice. Does anyone have any input on the EMF factors / benift of an iron or steel top plate? I intend to mount the choke below the plate, but hopefully orthoganal to the other two transformers. Will EMF (etc) be an issue?

Much earlier in this thread I asked about the brand of 6SL7 I should run in these amps. There were many good suggestions made, but I still haven't acted on acquiring them. Does anyone have a pair of 6SL7s they would like to part with?

As an asside: After struggling with panel punches and drill bits for the better part of a Sunday last month, an idea that I had well over a year ago re-surfaced: Pre-made metal top panels for the DIYTube products. I mentioned this idea here several months ago, but never took it any further. If you're interested in a water-jet cut metal top plate please read this message that I posted in the "prebay" forum earlier this evening: http://www.diytube.com/phpBB2/viewtopic.php?p=3359#3359

Thanks guys!
drew*

[nineno]

I've been chatting with Thermion this week as he is planning an all octal Ike pair. Using the stock values you can plug a 6SL7 in there (just set the Y & Z jumpers the other direction). BTW, note the placement of the 'keys'.

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):
1 -> *
2 -> 1
3 -> 2
4 -> *
5 -> *
6 -> 4
7 -> 5
8 -> 6
9 -> 7

I noticed (using a multi-meter) that pin 5 on the 12AX7 seems to be tied to pin 7 and 8 of the 6SL7...what's that all about? Isn't that a short circuit across the two heater pins for the 6SL7?

But it seems like it should go like this (12AX7 to 6SL7):
1 -> 2
2 -> 1
3 -> 3
4&5 -> 8
6 -> 5
7 -> 4
8 -> 6
9 -> 7

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

HELP!...

Thanks (as always) guys,
drew*