[dBel84]

hope it works as planned, post a few pics too..dB

 

[philodox]

Most attenuators go on the input of the pre, but there are some that go on the output... though that is rare. I'd double check with Broskie or look to see if you can find any info on tubecad to be sure though.

 

[Sarchi]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif just pulled up tubecad to get a visual of what you're talking about - sounds like you are hooking up the 12V SLA's in parallel to give you ....12V , try putting them in series : + from SLA 1 to J4, - from SLA1 to + of SLA2 and - of SLA2 to centre tab between J4 & J5. Make sure yuo are getting the 24 + V from the ends of the series batteries before hooking it up - you should be good to go..dB

dB - I did it and couldn't get a voltage measurement no matter what I tried, my voltmeter just read '1 .' ... So I took a deep breath and hooked up the clips; plenty of glow from the tubes now (i.e. 'normal' looking), still no sound and still can't get a voltage reading. The tubes started getting pretty warm...I started poking around with my voltmeter on the output end of things, got some crackle in my speakers doing that...both channels "work", yeah. Then I measured the voltage on the filaments -- V1 measured 6.8, a bit higher than I want but expected since my batteries are high at 14V. Now V2 -- 14V!!! Quickly unplugged the clips, omg my blood pressure. whew

The circuit was live for maybe 5-6 minutes all told. No sign of any damage. I DON'T believe V2/V4 should have that much voltage tho??? I thought all 4 run at 6.3V... the circuit is for 4 x 6GM8/ECC86.

I'm wondering-- is it possible JB omitted a step, should H+ and H- be jumpered together perhaps? Normally, J4-5 would be for 6.3V operation. But not in the case of running the heaters in series. (those familiar with the tubecad post 0057 will know what I'm refering to)

Thanks again for your help guys..it feels like I'm almost there, just something minor/obvious to figure out..

 

[dBel84]

I am having a hard time trying to visualize the jumpers without seeing the pcb. The H+ H- should not be jumpered. J5 is what is not clear at the moment - does J5 connect to H+? if so then make sure that you connect the batteries to J4 and the pin between J4 and J5. How are you measuring the heater voltage - the best way would be as indicated on Broskie's web page - With the negative probe on gnd (centre point between J4 - J5) measure J2 = 18V, J3 Right = 12V, J3 left = 6V , J1 = 12V . I hope this makes sense to you..dB

 

[kipman725]

Running any amp of battries is a bad idea. A regulated DC supply can have an output impediance (by using feedback) as low as 0.0001ohm wheras battries have output impedances of several ohm's at least. This means that the more current your amp is using at a point in time the lower the supply rails are. This means that the bigger drum hit or whatever you have the lower the supply rails sink which means that your sound will become load modulated. This is a bad thing as the amplifier will produce a more distorted output!

if you used a large capacitor bank with the batteries this problem would be reduced... but the question has to be asked... whats the point?

 

[Sarchi]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif I am having a hard time trying to visualize the jumpers without seeing the pcb. The H+ H- should not be jumpered. J5 is what is not clear at the moment - does J5 connect to H+? if so then make sure that you connect the batteries to J4 and the pin between J4 and J5. How are you measuring the heater voltage - the best way would be as indicated on Broskie's web page - With the negative probe on gnd (centre point between J4 - J5) measure J2 = 18V, J3 Right = 12V, J3 left = 6V , J1 = 12V . I hope this makes sense to you..dB

I'll unscrew the pcb and get some pics of both sides. I also emailed John last night for some advice.

I reconnected the batteries and measured DC voltage per your post, I got: J2=7V, J3 right=3.6V, J3 left=7V, J1=7V. In my other post above, I was putting the neg probe on the same ground, but the pos on pin 5 of the tubes (filament).

 

[Sarchi]

OK..here are two pics of the breadboard, finally.
Note that I have my power leads inverted as far as color-coding. I AM observing correct polarity.

Also note, H- has two pads (vertically), one is hidden behing the red power lead.

To answer dB's question...J5 does NOT connect to H+, as far as I can see. The pcb has two layers of traces, I hope the pics don't add to the confusion.

 

[dBel84]

I sure hope those bare copper wires on the input/output have some form of invisible coating to prevent the input/output shorting to ground. I would strongly recommend teflon coated or shielded wire.

The only other thing that seems to be unusual is that your tube shields are not grounded - if I am reading the pcb correctly, you have added a star grounded the star ground. It would be neater and simpler to merely use a jumper across C3/C4 etc.

why not remove the input output leads from the amp board and measure again. You should note that because the heaters are hooked up in series, the current flows as follows pin4->5 V3 - pin 5->4 V4 - pin 5->4 V1 - pin 5->4 V2 - refer back to Broskie's diagram..dB

H- connects to J5 - my mistake

 

[Sarchi]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif I sure hope those bare copper wires on the input/output have some form of invisible coating to prevent the input/output shorting to ground. I would strongly recommend teflon coated or shielded wire.

It's RS magnet wire, I used it in my Bottlehead kits and didn't have a problem. The stuff is coated with varnish..a real PITA to work with.

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif The only other thing that seems to be unusual is that your tube shields are not grounded - if I am reading the pcb correctly, you have added a star grounded the star ground. It would be neater and simpler to merely use a jumper across C3/C4 etc.

As per Andrew's advice on page 1 of this thread.. " With a 6GM8 you can just use a wire for [C3 and C4] and directly connect the shield to ground. Not a bad idea really." So the zip cord you see is attached to both C3/4 pads and to a common ground point. I hope I didn't screw that one up.

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif why not remove the input output leads from the amp board and measure again. You should note that because the heaters are hooked up in series, the current flows as follows pin4->5 V3 - pin 5->4 V4 - pin 5->4 V1 - pin 5->4 V2 - refer back to Broskie's diagram..dB H- connects to J5 - my mistake

Thanks...I was really hoping this would be simple to solve, but unless JB reads this entire thread, I think I'll have to go back through everything. In any case I need to reverse my attenuator position.

Thanks for your inputs again.

 

[dBel84]

I think Andrew meant to jumper the Cap traces as they connect to ground, but either way works - I was thinking more along the lines that you may have connected the ground side to ground and not the side that connects to pin 9? ..dB

 

[fran]

I tried having a look at the pic above. I thihnk you'd need something in where C3 and C4 are, but also, it seems that you don't have anything connected to B+ terminal. Without this you won't get much sound!

Down further on that tubecad page is a schematic where he tells you how to connect up the heaters in series using a 24V supply - did you see that (ie not using H+ and H- using a jumper and bringing your heater supply to each side of another jumper and reversing the polarity of one of the heater caps on each side?)

He also fairly clearly states that as that circuit stands it wouldn't be suitable for headphones (hence the mention of a buffer circuit later)


I'm interested in this as I just received my mono aikido boards this week and the last of the components arrived today for my 24V 6gm8 aikido. I bought a 2A 24V power supply from ebay, gives me regulated B+ in can.

BTW JB mentioned that a lot of people had been asking for a headphone version of the 24V aikido and he is strongly thinking about making a stereo PCB for 6GM8 use with a BUF 634 integrated into the board. I told I' buy one!

Fran

 

[fran]

Duplicate, got a AKG ad and thought I'd lost the post, wouldn't show up when I went back to reread it.

 

[Sarchi]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif I think Andrew meant to jumper the Cap traces as they connect to ground, but either way works - I was thinking more along the lines that you may have connected the ground side to ground and not the side that connects to pin 9? ..dB

Ah.............thanks for the clarification. I did do that! That's where I'll start with the "undoing" then.

 

[Sarchi]

Quote:

Originally Posted by fran /img/forum/go_quote.gif I tried having a look at the pic above. I thihnk you'd need something in where C3 and C4 are, but also, it seems that you don't have anything connected to B+ terminal. Without this you won't get much sound!

The cognescenti here figured I could just jumper C3/4 to ground with the 6GM8 circuit. As for B+, if you look at the underside you'll see the trace - it's tied to the smallest cap C5, which connects B+ to ground. The schematic shows B+ going to "+24V", but I think it's ok as is. (?)


Quote:

Originally Posted by fran /img/forum/go_quote.gif Down further on that tubecad page is a schematic where he tells you how to connect up the heaters in series using a 24V supply - did you see that (ie not using H+ and H- using a jumper and bringing your heater supply to each side of another jumper and reversing the polarity of one of the heater caps on each side?)

Yes...it's all in the posts above.

Quote:

Originally Posted by fran /img/forum/go_quote.gif He also fairly clearly states that as that circuit stands it wouldn't be suitable for headphones (hence the mention of a buffer circuit later)

Right, I'm using this as a linestage, not a headphone amp.

 

[fran]

Yep, I think the C3/4 thing only helps with hum.

The B+ thing: I can see that C5 couples it to ground, but where have you got your 24V supply actually connected in? Maybe I'm getting confused cos I can only see your heater supply connected up in the photos in the earlier posts - the 24V B+ supply doesn't seem to be connected in at all. Prob just my late night reading of the photo though!!!

Must go to bed....