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Old 15th March 2009, 11:45 PM   #1
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Default Parts mined from an AKAI 1800L, what to do?

Hello.

I haven't tried anything with tubes, but I want to get in on that "tube" sound, and managed to get these parts from a broken cassette player. I think these are the original tubes.

12AT7
6CA4
3x6AR5

Looks like enough for a stereo single-ended amplifier. I'm not messing with preamps yet, since I don't need them.

These were driving 2 25W speakers, transformer isolated.

I read on wikipedia that the 12AT7 is more suited for high-frequency use and has lower transconductance than the 12AX7, which is more commonly used for audio.

If it's a faster part, maybe we can get away with higher open-loop gain (if anyone does any of that when designing with tubes ).

Anyways, I am mainly looking for a good amplifier that will allow me to experience the tube sound but with decent sound quality that will allow for use as perhaps my main listening amplifier (anything that sounds better than my cheap stereo). I don't know what all can be done with 2 tubes per channel, but I don't really know anything about tubes. I could also go tube-transistor hybrid, to step up the output power.

I have the original power trafo, all caked with mud, and I hope it won't explode if I try to plug it in. Maybe I should try soaking it in vinegar or something. Will it work after who knows how many years in rain and winter?

I have the original boards and all the components on them, which should minimize what I have to buy online.

Can someone point me to a project that will work with the devices I have?

Thank you,
- keantoken
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Old 16th March 2009, 12:39 AM   #2
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The valuable parts you salvaged are the three transformers- assuming they work ok.
I wouldn't soak the power transformer in water/vinegar- no! Clean them up and even dry them in a warm-not hot- oven if you think they are damp at all.

You need to know what you are doing to work on these things safely, so I will not say much more.

If you can find a small 'wall-wort' AC adapter that outputs 10-20 v AC, you can use that for testing your transformers.

Those tubes are not very valuable so I would not be limited to using them, if I were you.

Something like the RH84 amp by Alex Kitic would be a good bet.

Cheers
John
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Old 16th March 2009, 12:50 AM   #3
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Alright. I guess I can't make plasma tweeters, can I?

Thank you.

- keantoken
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Old 16th March 2009, 03:30 AM   #4
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1/ Alai 1800 is a reel-to-reel

What you probably want to do is recreate the SE amp that was in the Akai.

6AR5 is fairly common in Japanese kit (i have parts for a pair of monobloks). 12AT7 will be just fine for driver. 6CA4/EZ81 is fine as a rectifier.

Click the image to open in full size.

I'd try wiring it like an RH84... you'll get maximum power while retaining good sonics.

Finding a choke for the PS would be a good idea.

dave
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Old 17th March 2009, 12:14 AM   #5
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Is it important to give the heating filaments a regulated supply or can I just connect them to the AC? How much hum will be present?

Also, I can't find a manual for the 1800L without having to pay. Can anyone send me one?

Thanks,
- keantoken
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Old 17th March 2009, 01:08 AM   #6
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Quote:
Originally posted by keantoken
Is it important to give the heating filaments a regulated supply or can I just connect them to the AC? How much hum will be present?

Also, I can't find a manual for the 1800L without having to pay. Can anyone send me one?
AC heaters is fine...

You don't really need the manual... the amp you want to build is pretty simple... this is the one i'd start with... you could probably get away with just changing the size of the cathode R on the output tube -- maybe on the driver if the B+ you end up with is way different.

Click the image to open in full size.

Tubes are pretty forgiving.

dave
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Old 17th March 2009, 11:26 PM   #7
kevinkr is offline kevinkr  United States
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Hi Dave,
Apparently that link is not directly viewable, and there is a quite strongly worded upgrade notice instead.
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Old 18th March 2009, 02:30 AM   #8
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Stuck in my browser cache... went to a different browser to see the remote linking message... i moved it over to some of my web space & fixed the link.

dave
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Old 18th March 2009, 04:01 AM   #9
kevinkr is offline kevinkr  United States
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Looks good, wondering how you posted the pictures so the background doesn't show?

I should build me a similar amplifier, (I've got Nord Mende transformers, and Tele 6BQ5s - should be a nice and I am currently contemplating building a pair of Fonkens in the near future.. (I have a very large pair of Onkens in my main system so the Fonken seems like a natural.. )
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Old 18th March 2009, 04:36 AM   #10
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Guys,

It should not be especially difficult for keantoken to map the RH84 design onto the "iron" and tubes he already has.

Based on the 6AR5 data sheet Dave (planet10) provided, the B+ rail will be "shorter" than that shown for the 6BQ5/EL84 setup. Would 10M45S CCS loading be a good idea for keeping the gain of the 'T7 section up, at a lower drop in the load? "Check valve" style decoupling between "finals" a voltage amplifiers is another way to hold losses down.

BTW, does anybody know what Akai used the 3rd 6AR5 for? Regulator? Bias erase oscillator? ...
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