[fierce_freak]

I've been intrigued by using the 6GM8 during the past week or so. I've been reading up on tubes quite a bit in the past two months as I've never built a tube-based amplifier. I thought using the low voltage 6GM8 could be fun for a first project, to get me started. Of course, just because it's my first tube amp and a warm-up, I don't think it has to be a bad amp.

I'm open to hybrids, too. The Aikido with a buffer is an interesting option, and there are a couple other designs that look good, too (EHHA and others). Anyone have any thoughts on the best amp circuit to build around 6GM8?

 

[Sarchi]

This tube was made to be used in car radios, though they must have had some damn sensitive speakers to get any juice out of it as a voltage amplifier. I'm aware of the Aikido 24v (I built it, and sold it to a friend), and also Welborne's Ultrapath battery linestage, which I think uses the same tube. That's about it.

p.s. I searched the Sound Practices cd (744-page pdf), nothing there.

 

[pinkfloyd4ever]

there's this that Pete posted way back (prolly in the spring) in the MAX thread, but I don't know what the status is on whether/when boards are being made

 

[tomb]

Quote:

Originally Posted by pinkfloyd4ever /img/forum/go_quote.gif there's this that Pete posted way back (prolly in the spring) in the MAX thread, but I don't know what the status is on whether/when boards are being made

I'm hoping we'll make boards available for that eventually. I'm having trouble talking Colin into any interest in a speaker amp. I think if you combined that thing with some $49/pair Sony, Pioneer, or Infinity small bookshelfs from Circuit City or similar, you'd have a nice setup. We will be investigating it, for sure.

As for the 6GM8 - Dsavitsk can probably tell you a lot more about it. He actually designed a little amp for it on the DIYforums.org site. It's in a sticky thread called the MEHA. It's an excellent quality tube that's pretty much made to operate at the same plate voltages as Millett tubes. However, the heater uses 6.3V at twice the current of both Millett tubes (it's also a 2-channel tube), so it has some inherent issues to overcome to make its use convenient.

 

[fierce_freak]

Yeah, I was considering running a 24v aikido with 6GM8's off of amb's sigma22 at +-12v so it wouldn't be too difficult to bolt a ss output buffer on it. The four tubes' heaters could be ran in series off of the s22 for 6v each.

-edit- i was considering doing the standard hybrid deal and just attaching some jisbos buffers on the output, but I wanted to see if there were any other cool designs and if anyone had any experience with it driving headphones. I've seen dsavitsk's MEHA, and it looks pretty cool, too.

 

[tomb]

Quote:

Originally Posted by fierce_freak /img/forum/go_quote.gif Yeah, I was considering running a 24v aikido with 6GM8's off of amb's sigma22 at +-12v so it wouldn't be too difficult to bolt a ss output buffer on it. The four tubes' heaters could be ran in series off of the s22 for 6v each. -edit- i was considering doing the standard hybrid deal and just attaching some jisbos buffers on the output, but I wanted to see if there were any other cool designs and if anyone had any experience with it driving headphones. I've seen dsavitsk's MEHA, and it looks pretty cool, too.

Yep. Suffice to say that it may be the highest quality tube available at these voltages - period.

EDIT: If I'm not mistaken, Runeight's EHHA uses the 6GM8. According to dBel, it may be the highest quality hybrid available. The Sigma is a definite requirement, I believe.

EDIT2: I think they had some early teething problems. Maybe they got those fixed, but it's hard to tell - Runeight went private to protect his designs.

 

[ericj]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif EDIT2: I think they had some early teething problems. Maybe they got those fixed, but it's hard to tell - Runeight went private to protect his designs.

You have to admit, though, you'd be shy of showing your best work-in-progress in public if some guy in china grabbed an unfinished design, put it in production with mistakes in the silkscreen, and then thousands of n00bs expected you to support their efforts to use the board.

 

[tomb]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif You have to admit, though, you'd be shy of showing your best work-in-progress in public if some guy in china grabbed an unfinished design, put it in production with mistakes in the silkscreen, and then thousands of n00bs expected you to support their efforts to use the board.

Yeah, that pretty much says it.

Even though I know the history (and it's much worse than I knew at the time), it's difficult to fathom the reason behind the fixation on Runeight's designs - to the exlusion of anyone else's. You can look in the other guy's online photo storage and find versions of almost everything Runeight has going. It would scare anyone who puts in the time and investment that it takes to bring one of these designs to the community. (I have a little better idea now of what that entails.

)

If the practice spreads, it will have a paralyzing effect on the DIY community. No one will ever want to publicly share a design for comment and user improvement - sort of removes the wonderful part of collaborative effort that has existed up till now in the community.

 

[Andrew*Debbie]

Quote:

Originally Posted by Sarchi /img/forum/go_quote.gif This tube was made to be used in car radios, though they must have had some damn sensitive speakers to get any juice out of it as a voltage amplifier.

I've repaired a few car radios that used low voltage tubes. They were all hybrids. A single power transistor drives the speaker. Far from high fidelity.

Earlier car radios used high voltage tubes and an output transformer. They were much like the table radios of the day.

Ditching the high voltage power supply made the radios smaller and less expensive.

 

[tomb]

Quote:

Originally Posted by Andrew*Debbie /img/forum/go_quote.gif I've repaired a few car radios that used low voltage tubes. They were all hybrids. A single power transistor drives the speaker. Far from high fidelity. Earlier car radios used high voltage tubes and an output transformer. They were much like the table radios of the day. Ditching the high voltage power supply made the radios smaller and less expensive.

Except that the older radios used troublesome vibrators to get that high voltage.

 

[dBel84]

I won't blather on but suffice to say that all problems have been ironed out and head over here if you want to read a little more on the subject.

I am not sure about TomB's quoting me as saying it is the best hybrid out there but I am sure it is on par with any top rate amps on offer (DIY and commercial). It doesn't necessarily need the S22 but the better the power supply the better the overall performance and as AMB has made such an advanced supply available to us at relatively little cost, it makes good sense to use the best available..dB

EDIT: before people think that there were actual problems with the design - my build suffered from incorrect resistor selection, the other prototyper's suffered no such folly.

 

[fierce_freak]

Yes, I was considering the EHHA and saw the web page for it last week. It's good to know the problems are ironed out. Looks like I have a couple options to consider...thanks guys!

 

[SnoopyRocks]

Quote:

Originally Posted by tomb Yep. Suffice to say that it may be the highest quality tube available at these voltages - period. EDIT: If I'm not mistaken, Runeight's EHHA uses the 6GM8. According to dBel, it may be the highest quality hybrid available. The Sigma is a definite requirement, I believe. EDIT2: I think they had some early teething problems. Maybe they got those fixed, but it's hard to tell - Runeight went private to protect his designs.

Quote:

Originally Posted by fierce_freak /img/forum/go_quote.gif Yes, I was considering the EHHA and saw the web page for it last week. It's good to know the problems are ironed out. Looks like I have a couple options to consider...thanks guys!

It's amazing how those who were not involved ostensibly know more than those who actually were. Perhaps both of you could enlighten us all as to what really went on. I'd like to know what I missed.

 

[tomb]

Quote:

Originally Posted by SnoopyRocks /img/forum/go_quote.gif It's amazing how those who were not involved ostensibly know more than those who actually were. Perhaps both of you could enlighten us all as to what really went on. I'd like to know what I missed.

Yes, well some of us can read. dBel did have problems initially. As for you, as far as I know - despite your obvious excitement in your posts in that thread - you never posted the results of your build, never posted pics, and never posted in that thread again.

If I'm incorrect in these facts, then accept my apology. Otherwise, give a little bit of credit to other people without the patronizing.