Amp Deal of the Century!

fredv

Good catch, I use FF and didn't know IE would render gif, sorry guys.
Try downloading it to disk, and then use Microsoft Photo Editor to open it.

I purchased the tubes from www.thetubecenter.com. Jack is a great guy to deal with, I purchased the 6GM8's along with some 5687's for an average of about $5 each shipped, and they are NOS. My 6GM8 happens to be Amperex, made in Germany!! Literally, that's the only parts that I had to purchase, I had the rest in my parts bin. Jack also has tube socket, so you can purchase one at the same time, about 2 bucks. Here are the parts list:
1. 6GM8 tube x 1 (I recommend to buy at least a couple just in case, you pay
very much same amount of shipping anyway). I bought 4, the 1st one that
I picked worked the magic right from the beginning. Since this is low voltage,
you can use it to build a computer preamp using the desktop power supply!!
2. 1 x 100 ohm resistor
3. 1 x 4700V 25V electrolytic cap (>= 2200uF 25V, I just happened to salvage this from an old computer PS :-)) #2 and #3 are to add a little more filtering to eh +15V.
4. 2 x 1200 ohm resistor (plate resistors)
5. 4 x 1M ohm resistor (anything >= 470K will work, I use 520K and 2M, ran out of 1M in my parts bin :-))
6. 2 x 180 ohm resistor (cathod resistors 180 <= antyihg <= 200 will work)
7. 2 x 47uF 25V electrolytic cap (optional, used as bypass in the cathode)
8. 2 x 0.1uF cap (coupling cap to the amp section, anything rated > 25V will do)
9. 2 x 1K resistor (grid stopper)
10. 2 x 0.01uF disk cap (>= 16V, this is to shunt the nosie from the AC to the heater).
11. 1 x 100K dual audio taper pot.
12. 1 x 117V pri, 6.3V sec tramsformer, mine is a triad rated at 0.6A in the secondary (the heater will draw 0.33A).
13. 1 x 9 pin socket.
14. 2-3 ft of shielded cable.
The rest is pretty much using whatever you can find to put everything together. If you are interested in building one, PM me you address, I will send you whatever spare parts that I find.

edit: Try this image to see it is better ....

engtaz

That works in opera and IE.
thanks

madmax

Just thought I would point out something I noticed about the Accurian. It sounds poor for the first 15 minutes or so until it warms up a bit. Anyone else notice? Although not a stretch of the imagination that warmup causes good things to happen I found it overly noticeable on this amp.
madmax

madmax

fredv wrote: »

edit: Try this image to see it is better ....

I printed it and enlarged it but still can't read. Why is it so small?

fredv

madmax wrote: »

I printed it and enlarged it but still can't read. Why is it so small?

Too much compression from MPE. OK, I hope 3 is a charm :-)

fredv

madmax wrote: »

Just thought I would point out something I noticed about the Accurian. It sounds poor for the first 15 minutes or so until it warms up a bit. Anyone else notice? Although not a stretch of the imagination that warmup causes good things to happen I found it overly noticeable on this amp.
madmax

I did notice what you observed - improve after warm up, sounded a little more rich vs thin when cold. I thought it was related to the components were still new. The warm up does make sense. When the caps are fully charged, there will be more stable power supply which always translate into better sound.

Polk65

Looking good Fred. What's next, power transistors change?

fredv

Change the power transistors is a little more work now due to the molding formed around the added pot. Once the hot glued molding is ermoved, the whole tube preamp can be taken out by unscrew it from the standoff's below. Eveything is sitting on the plastic board. I bought 2 Accurian's, maybe I can mod the 2nd one's amp section to see how far it can go. Worst come to the worst, it blows, and I will reuse the toroid to build a mini aleph or gainclone :rolleyes: I will bring this amp to the BA gethering for your audition.

engtaz

fredv thanks,
Let us know if you have anymore tweaks. what size was your board you mounted all the components onto and what about the metal plate you have the tube on?

Question question who's got a question.
Sorry just very inquisitive about your work.

fredv

The transparent plastic board is about the same size as the receiving board that I removed. Maybe half inches wider and longer on each dimension, the more space the better, obviously :-) This tube can be mounted in any position, I found mounting it side was the most convenient to soldering the pins. I just happened to have such aluminum bracket from a parts out oscilloscope. You can use thick cardboard and some small right brackets to mount the cardboard vertically to the plastic board. If you can find a metal sheet, say 1.5" x 4", you can simply bend it into a right angle bracket for the tube socket. The aluminum housing that I use is indeed too big that waste a good chunk of workng space there. Also, the heat sink at the back also can be used to help securing the mounting firmly as well. As a matter of facts, I spent a lot of time to find the "right junks" and to figure out how to place them in this 4x5.5 board, and my pride I was when I pointed to the amp and told my wife, "See, those are the junk that you told me to throw away " Here are a few more closeup, I hope these will help.

engtaz

fredv,
How is it sounding to you after breakin period. Any new tweeks.

Thanks

Polk65

I stole two demo models yesterday at $10 each. One is going on my workbench and the other for road trips testing used speakers. Check their web page with your zip code to find which stores nearby still have them.

madmax

I just wanted to report in. No tweaks to mine but it has been left on since the day I got it, no problems yet.

Man, I can't wait until some time frees up so I can add a tube to mine.
madmax

fredv

Hi Roy,

No, I didn't tweak the amp since I put in the tube. I am using it with a pair of monitor 5's. The tube pre seems to tame the SL2000 quite a bit, the mid and the high are very smooth whereas there is not much in the bottom. I suspect the amp circuitry is designed to attenuate the lower frequency so that it can achieve the 25W rms rating. It is the stereo of the choice instead of the bigger rig when I am working from home.

It takes a little time to find and to fabricate oddities to put the transformer and tube in place. It is well worth the time. I'll bring this amp to the Bay Area Polkies gathering in June/July so that Steve can also audition and comment the difference.

Refefer

Polk65 wrote: »

I stole two demo models yesterday at $10 each. One is going on my workbench and the other for road trips testing used speakers. Check their web page with your zip code to find which stores nearby still have them.

FYI, they're going for 30% off now, I scored 3 for a little over $30.

engtaz

fredv wrote: »

Hi Roy,

No, I didn't tweak the amp since I put in the tube. I am using it with a pair of monitor 5's. The tube pre seems to tame the SL2000 quite a bit, the mid and the high are very smooth whereas there is not much in the bottom. I suspect the amp circuitry is designed to attenuate the lower frequency so that it can achieve the 25W rms rating. It is the stereo of the choice instead of the bigger rig when I am working from home.

It takes a little time to find and to fabricate oddities to put the transformer and tube in place. It is well worth the time. I'll bring this amp to the Bay Area Polkies gathering in June/July so that Steve can also audition and comment the difference.

Changing the Moniter 5's with RDO194's is a must. The sound difference is silky smooth vocals.

fredv

Where did you see the 30% off? The RS web still list at 14.95. The RS store nearby still has some in stock, according to their website. Maybe help them to clear all if they give me 30% off ..... Can't even buy the toroid's at this price!!!

Refefer

fredv wrote: »

Where did you see the 30% off? The RS web still list at 14.95. The RS store nearby still has some in stock, according to their website. Maybe help them to clear all if they give me 30% off ..... Can't even buy the toroid's at this price!!!

Give them a call, and they'll look it up for you. The only RS near me that had them in stock gave me the discount at the register when I picked them up an hour or two ago.

Polk65

Just a reminder that if you are buying a couple of these, pop them open and have look inside. I found one with a pinched power wire and the photos are in post #35.

Danny Tse

How do you get the 30% off discount?

I picked up 2 of these amps this afternoon and they rang up at $14.97/each.

Refefer

Huh, that's strange. The store I went to said that RS was in the final stages of liquidating this stock and were giving serious discounts.

Strange.

bundee1

Are there any mods or tweaks to get the frequency range to 20HZ to 20KHZ?

madmax

bundee1 wrote: »

Are there any mods or tweaks to get the frequency range to 20HZ to 20KHZ?

What is it now?
madmax

hearingimpared

bundee1 wrote: »

Are there any mods or tweaks to get the frequency range to 20HZ to 20KHZ?

???????

Polk65

50Hz-20K per the manual. There is speculation that this may be bypassed in the pre stage.

8 ohm loads are good to go. 6 ohm loads will kick dust but occasionally shut it down. My next mod will be to change the power transistors.

These have become scarce in the past two weeks. Buy now if you are interested. At $15 it's a no brainer.

cmy330go

aris wrote: »

sold out on the website

Um.....Pretty sure they were sold out online before this thread was even started.

madmax

Yea, they were. Mine is still on and playing its heart out.
madmax

fredv

I was bored, and I took mine apart last night for the sake of "see what exactly this thing is".

I think the tranny is good for what it does, replace the output transistors tip42c/tip41c pairs will probably improve the reliability (won't burn out as easy if you accidentally crank up the volume with a low impedance speakers) won't won't give you more output power. I will say, don't touch it until it is bead

Given the power supply is only a capacitor (6800uF, one per rail) after a single bridge rectifier, I am pleasantly surprised the low ripple noise!! Maybe there is some noise rejection circuit downstream, need to look at it further.

Polk65

Fred, keep probing.

This is ~9 months after RadioShack's web site sold out. Check their product page (scroll down to 'other ways to get it') and enter local zip codes or call your local stores. http://www.radioshack.com/sm-accurian-homeplug-digital-audio-receiver-amplifier--pi-2049804.html

Chuck is tuned in. Fred is asking why. I plan on creating a gainclone from the parts, or at least a good explosion.

fredv

Polk65 wrote: »

I plan on creating a gainclone from the parts, or at least a good explosion.

The tranny isn't the best fit but can be done. Let's chat more this Saturday. FWIW, I already have 2 GC channels soldered up, I just need to build a PS specific to this transformer