Home » Audio » Thermionic Emissions » 6Ah4 Amp
6Ah4 Amp [message #11326] Wed, 28 June 2006 16:58 Go to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Well; I don't know who cares about this old tube but I am now in the process of gathering parts for a SE amp built from this tube.
Before i ramble on with this I'll state that I was following Damir's project on the group build section where he has built a 300B SE amp. His project looks to be probably about as good a design as is possible to make. Someday I would love to explore that opportunity but right now the over 1K$ in parts alone is just not happening.
So in perusing the web I came across a very simple and nicely done amp using the 6AH4 as a power tube and the 5755 as a driver with a 6X4 rec tube. The voltages are manageable and the parts count is low and a couple people have expressed delight in the sound of this amp.
The 5755's were 4$ each. The 6Ah4's were 8.50$ each and the 6X4 was 9$.
It uses a 7kp output trans and a 500v ct power trans along with a 10H filter choke. I have the choke from Hammond and the power trans is a 372x. I just need some advice on what output trans to use; prefferably something that can be re-used for a better amp someday if needed.
I bought a Hammond chassis and am using the Ratshack 100K pot. The rest of the parts are pretty cheap; I think I can do this for under 400$.
Just thought I'd post on this since there hasn't been much activity on the SE forum lately.
I am building this to run with my little Ion BS 1's SD speaks with a tweeter that comes in at about 8k.


Re: 6Ah4 Amp [message #11327 is a reply to message #11326] Thu, 29 June 2006 20:25 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
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Registered: May 2009
Master
Hi M,
I am not familiar with the 6AH4, so I looked it up in my trusty ‘GE essential characteristics’ ( a great quick reference book by the way).

The kicker here is the high plate resistance (Rp), requiring the < 7K transformer. Most of the good affordable multiple tap transformers, like the Lundahl or James run about 3K to 6.5k. The higher K transformers tend to be for the high power triodes like the 845, so get expensive.

If the designers feel that 6.5K will do. The James transformers at about $150- $200 a pair are a fine choice and will be right at home in any number of future amps. I have a pair in my DRD amps.

If 6.5K is to low, or over budget, take a long look at the Hammond 125 series. At $20-$35 each, they are not the last word in thunders bass, or shimmering highs but are pretty pretty damn good for the money. Have a look at Angela. http://www.angela.com/catalog.html
Keep in mind that I would not expect more than a 1-1.5W with this tube. So thunder is probably not in the program.

I don’t want to dissuade you from your project but have you considered the 2A3, at about $30…John


Re: 6Ah4 Amp [message #11328 is a reply to message #11327] Fri, 30 June 2006 07:20 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Thanks John thats excellent help. I knew about the high Rp and the 7k trans. I figured that would lead to eventually a big triode amp. That has always been my goal except I felt I needed more experience to work with the high plate voltages.
The speakers for this amp are very efficient so 2watts is adequate. I have to e-mail the amps designer and ask what he thinks of the 6.5k trans. They use I believe Hashimoto trans?
How you doing with the Broskie pre-amp?

Re: 6Ah4 Amp [message #11329 is a reply to message #11328] Sun, 02 July 2006 11:21 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
Hi M, If a big triode amp is the goal. Consider whether or not a 3-6.5K mid sized transformer would be usable. I know an 845/211 wants about 10K and about 20-30 Watts as well. I have not looked too far into the world of big triode amps, the high voltage scares me too. I have not done enough research to say what tube might work with what transformer.
On the other hand, Ray P of the DC Bottleheads, built a 829 amp that uses a Radio shack 70V line transformer Parafeed. This trans is about the size of an ST-70 chock and it sounds great. go figure.
Go to the Bottlehead forum, search Under Ray P and Meet pics. It’s worth a look.

So for the 6ah4 the little Hammond’s might be the way to go. Another possibility, if you have a set of P-P transformers handy from say a EL84 or 6V6 amp, these run about 6-8K. Yea I know a P-P trans is not designed to run single ended and you will saturate the core, at least somewhat. But at very low power it works.

As for the Aikido, I have not done anything new with it. It works POS power supply and all and I have lately been spending my time on my 300B amp, when it is cool enough to run it (92 here in Valley Forge today). there is more over at G.B…John



Re: 6Ah4 Amp [message #11330 is a reply to message #11329] Sun, 02 July 2006 18:37 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
92 in the shade? I have no problem paying for a good set of trannies if I have to. Let me ask; is the 300B your tube of choice? I only ask out of curiousity; seeing as how they are so darned expensive. There are so many amps oput there; how to tell what tube is your choice??

Re: 6Ah4 Amp [message #11331 is a reply to message #11330] Mon, 03 July 2006 16:40 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
Well, you might say the 300b is my tube of choice, because, I have a pair.

When we talk of common DHT for SET amps we, (I) mean 45, 2A3, & 330b.

I love the 45. My 45 DRD is probably the most "refined" amp I have but with my 96db speakers, they are more than sometimes, not enough. Even at very moderate volumes.

OK, flashback time. A few years back, when I thought to try the SET thing, I, as I suggested above tried it by inflicting it on my long suffering ST-70. I wired one EL34 across both sides of the output trans and let her rip. I liked it enough to pursue the idea. I had less efficient speakers back then and was used to 20-50W of P-P tubes and 250W of SS. So the 300b seemed like the only choice.

The 300b has the most output power, they say 8W into a 3.5k load. I use a 5.6k load for about 4~5W and it’s still plenty.
But the 300b is a hard tube to drive. So (in my opinion) it’s sound ,is more dependent on the input stage. I have tried .
FI, OK but soft.
SSRP, just couldn’t get it to work for me.
WE-91(6sj7) not bad at all, may well be many people’s cup of tea. If I had the money I’d try 310’s.
DRD,I was still on the 45 honeymoon, so not a fair trial, must get back to that.
And now the choke loaded D3a. This is working for me so far. What I am looking for may not be the "best". What I Want is a sense of life or emotion. Not something pure but clinical like a gain clone. (though I will not part with mine)

Some reviewer once said something like "the 300b sounds great but you always know you’re getting a show"

I was playing some James Cotton a wile ago and I was at the show.

On to the 2A3.

2.5 Watts.

If this is enough power for your speakers. It’s pretty much a ‘no brainer’ They are not too expensive and easier to drive. There are so many kinds out there both, new and old you can tune the sound a little

If you have high efficiency speakers, that’s what I’d do. If you have a 3-5K transformer you can try something else later…John





Re: 6Ah4 Amp [message #11332 is a reply to message #11331] Tue, 04 July 2006 18:02 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Here's why I ask. I lived with an EAR 859 amp for a couple few years. Thats an SE using a 509 pentode wired in triode. Very good Yoshino Transformers driven by 6922 tubes. The sound was very good but dry; very dry. Thats why I sold it. Yet lots of folks love that amp and that combination. 300b's sound exactly to me like you say; very 3d presentation; we call it pschycadelic. 2A3's are too soft. Thats why I am trying the 6Ah4. I figure something has to have that lively/detailed/good bass; vintage sound. Where instruments don't seem to be larger than life.
Thats what the 211's seem to do. except I'm too chicken to try them.
So is that where you are going with your driver stage?

Re: 6Ah4 Amp [message #11333 is a reply to message #11332] Tue, 04 July 2006 21:21 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
Pschycadelic; now there’s a cool word.
I am not familiar with that amp or the 509.
I tend to disagree with the 2a3 as soft.

The D3a is working well for me, I am still trying this and that. I am about due for an update over at GB, so I wont go into detail. To be honest this setup may be guilty of being a little bit larger than life. I will take them to the Bottlehead meet and see what everyone thinks.
I will have to revisit the DRD. What is now the DRD45 uses the James outputs and a really trick universal power transformer. But that is a project for a bit later on.

One thing I want to point out is this amp (the non DRD) has used the same power supply, 300b’s, and output transformers (Lundahl 1623) and by changing only the driver/input stage has turned it into 4 or 5 completely different amps. If I had started with the SSRP I may have given up on the 300b. Yet this works well for others.

I am curious as to who the 6ah4 will sound. Do you have a link to the schematic?

Happy Independence day…John


Re: 6Ah4 Amp [message #11334 is a reply to message #11333] Wed, 05 July 2006 08:38 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Hey John; here's the schematic.

Re: 6Ah4 Amp [message #11335 is a reply to message #11334] Wed, 05 July 2006 17:25 Go to previous messageGo to previous message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
Found it, Biglobe can be a pain.
Be sure try it with and without the feedback look.

If it doesn’t work out, consider the 6bm8 STC amp, from the same site and others. It would use the same power supply and chassis.

I built one and it is a great sounding little amp. My friend Dave prefers it to my other amps. hasn’t heard the new 300b yet…John


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