Antique Electronics Supply K-502 Stereo Amplifier update

Jstas

Ok, I think you have all seen the pictures and visited the link so I'll leave that out this time.

I finally recieved the Onkyo P-301 pre-amp and the Onkyo Tuner (T-4210). I also grabbed the Minetek DVD/CD/MP3...well, everything player that ATCVenom mentioned.

I hooked it all up and after finagling around with all the dials and buttons, bells and whistles, I finally got something that sounded decent. So, here it goes:

Minetek player:
- It has some audio tailoring features that will boost frequency response through what seems to be a crossover-network that loops back on itself. Effectivly creating what looks to be a passive, band-pass crossover network that while primitive by modern standards is clean and very effective. However, I believe that the pre-amp outputs are not of a high quality and they tend to be a tad dirty. Its not an isue though and for 50 bucks with shipping, its nothing worth complaining about. Defintly a steal. The major gripe I have about it is that you need a TV or monitor with a video RCA jack so you can see the menu/disc/track info. Kind of a bummer but again, for 50 bucks, I'll stop complaining. It is certainly not in the 50 dollar league and competes on clarity for both sound and picture with my 350 dollar Sony DVD player.

Onkyo Tuner (T-4210)
- Its nice and clean but I need a manual. Since I recieved it used, the old settings are still there and I believe that better peformance is available from it if I can get the thing reset. Otherwise, it pulls in far out stations, is not affected by things that totally screw up other radio units like RF intereference or EM interference. I need to get a decent antenna for it and when I do that, I think free is an awesome price for it! Yes, I got it for free. The lady was getting rid of it because of a divorce and she got the HT so she sold all of her husbands stuff. I picked up the tuner and pre-amp for 150 and that included shipping. Its about 500-600 bucks worth of Onkyo stuff.

Onkyo P-301 Pre-amp.
- This is a very nice unit. It has some signal tailoring capabilities but it doesn't emphasize the low end well when you turn up the bass knob. At least not to my tastes. Granted I don't want boom-boom but if I turn the bass knob all the way, I can't go real far with the volume until the signal stars breaking down. I thought it was the amp clipping but I was able to run a signal directly to the amp from the tuner and my Sony DVD player and I didn't have such problems until I reached a much higher volume level. Other than that, it is a very nice pre-amp and I think that if I can get a signal processor or equalizer, I can solve the excessive gain problem.

Overall, the amp sounds clean, clear and has power. The setup I have only cost me about 388 bucks with shipping and that includes the amp and speakers from George. I figure another 50 bucks for a Terk amplified antenna and whatever I can grab an EQ for off of Ebay and it should turn out pretty nice.

gidrah

Great reading my friend. I've narrowed down my next probable amp purchase to either this one or a particular 22w/ch solid state. The other will probably be 2nd though to be honest.

Jstas

Well, I just picked up this guy for 91 bucks plus shipping but he's in NYC so shipping should be cheap:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3271&item=3013790433&rd=1

Looks pretty cherry and reviews on it were pretty good. Lots of tuneability in it too so hopefully it will work out well for me. Got it for 91 bucks. Not too bad considering it was quite expensive when new.


BSR/ADC EQUALIZER W/SPECTRUM ANALYZER


I think I am done for now though. Since no recording equipment is allowed at my job due to security restrictions, I'm not going to worry about a tape deck. The pre-amp has like 6 different inputs so I have plenty of other spaces to stick stuff on there. When I get the EQ, I'll hook that up and see how it goes. Maybe it will make something better of a computer signal and I can tune in a web-broadcast radio station too.

Total price so far: $461 plus whatever shipping will cost me. So less than 500 bucks and I think its complete now.

My friend is going to be jealous. He thinks this rig already sounds better than his 850 dollar set of Polks and his 500 dollar Sony receiver. When he sees this EQ sitting on the stand he's gonna go ape-****!

gidrah

I've always wanted one of those.

Jstas

Originally posted by gidrah
I've always wanted one of those.

Are you for real or are you just being sarcastic? If you are then there were like 5 of them on eBay for less than 200 bucks. I got this one so now there are still 4 more. Might want to go and check them out.

If you are picking on me, I only got this because it was cheap and the reviews I read were very good so I figured it must be a good deal. For 90 bucks, why not?

gidrah

No I'm definately not pickin' on you. Put it this way; without opening the E-bay link, I'd say by the picture it is a BSR EQ-3000. It's a 10 band EQ w/ spectrum analyzer. It also comes with a calibrated microphone for the pink noise generator. They used to run a 2 page add for this puppy in Stereo Review (S&V) and the DAK catalogs.

They usually sell for between $110 and $60 on E-bay depending on condition and whether or not the mic and manual are present.

I've already got a couple of graphic and one parametric EQ. And my audio spending is currently topped out, but I WILL get one eventually.

Jstas

OK, I hooked the amp up to a 4 ohm load rather than an 8 ohm load. I don't know if the amp is 4 ohm stable or not but judging by the way it handled the 4 ohm load, I'd say it is!

Played it for about 2 hours with the amp volume set at about 3/4 full volume. It didn't get any hotter than it did with the 8 ohm load and it was just as clear and clean. It defintly has a bit more oomph running a 4 ohm load but that is to be expected.

I was driving a set of 6x9 Polk DX9's in particleboard enclosures.

madmax

Jstas

Well, it looks like I blew a tube. I switched it back over to the KLH 17's its hooked up to with the 8 ohm load. When I turned it on, the right side speaker made a snap sound and then the far right tubed glowed a bright blue. Not good. It could be one of two things. It could be the resistor that controls the polarity and impedance of teh circuit across the tube or it could be the actual tube. Since the two tubes for the right channel are wired to share polarity across the plates, if it was the resistor, both tubes would have died. So I'm guessing its the tube. I have new ones coming. They were only 6 bucks a piece so I grabbed so extras too.

What caused it? I'm guessing the 4 ohm load. It handled it ok when it was playing but I guess it was over-cooking the tubes and cause the filaments inside the tubes to burn off more than typical. So while the electronics could handle the 4 ohm load, it doesn't look like the tubes could stand up to the heat. Whether that is a tube quality issue or not, I do not know nor do i really care. I'm going to drive an 8 ohm load with them, I got this because it was cheap to experiment with so that's what I doing. I let everyone know what turns up when the new tubes show up in a day or so.

Oh, by the way, does anyone know where I could pick up a tube tester? I figured it'd be a good purchase if I plan on playing with tube amps for a while.

RuSsMaN

From a tube-idiot, mind you, but don't most tube amps have different taps for 4 and 8 ohm? If your amp only has one set of outputs, did the rectifier get damaged when loaded 4 ohm?

Talking out of my **** here, but thinking critically, I swear.

Cheers,
Rooster

gidrah

Sorry to hear about that. On the bright side the new tubes were cheap and swapping out might be a little fun. Out of curiosity, what brand did you get and of what style (part #)?

The 4 ohm load may have over cooked them, but I'd deffinately triple check all connections.

Jstas

Russ, All parts of the amp are integrated. There is no real "rectifier" assembly on the amp. Eveything was built by hand including the power supply. As long as the power supply can support the current draw, an amp can be 4 ohm stable. The issue I believe was the tube just flat out overheated. I think it may have been a problem waiting to happen because the right channel seemed to be a tad weaker than the left. It could have been a not-so-good tube from the start. What happened is related to a plate not necessarily burning out but rather, losing its polarity I guess you could say. It has to deal with impedance loads. I'm not too well versed on the operation of a tube because I don't have a whole lot of experience with it. From what I have seen though, impedance changes or even wiring a speaker out of phase could pop a tube. I think I may have reversed polarity on the right speaker by accident when I hooked the KLH's up again. I didn't have the problem until after I hooked up the KLH's. It did work for a few minutes before I got the pop. It could be the resistors that control the power and impedance going into the tubes but for one to be bad, it would show signs of damage and nothing except the tube looks to be bad. There are no foul burned smells coming from the amp either. I will have to test the potential of each lead on the board but I realy think the tube just went bad.


gidrah, I'm not sure what brand it is. I just got replecement tubes from Antique Electronics Supply to replace what blew. The tube number is 11BM8 and they have Made in Japan on the side of the ones that came with the kit. I don't know if the replacement will be a Russian or Japanese tube. I did not see a manufacturer name on any of the tubes though.

gidrah

Originally posted by Jstas
I'm not too well versed on the operation of a tube because I don't have a whole lot of experience with it. From what I have seen though, impedance changes or even wiring a speaker out of phase could pop a tube. I think I may have reversed polarity on the right speaker by accident when I hooked the KLH's up again.

gidrah, I'm not sure what brand it is. I just got replecement tubes from Antique Electronics Supply to replace what blew. The tube number is 11BM8 and they have Made in Japan on the side of the ones that came with the kit. I don't know if the replacement will be a Russian or Japanese tube. I did not see a manufacturer name on any of the tubes though.

You seem pretty dang well versed to me. Especially the possibillity of a connection problem. SS is much mor forgiving and less lethal.

I'd assume you'll get Japanese tubes in replacement. If you plan on upgrading, Sovtek and Electro-Harmonix seem to be well received for the tubes I look for. Unless I happen across a quad set of NOS Mullards for about 1/10th their going rate, one of these will be my next choice. For now mine are fine though.

madmax

I'm still trying to figure out if I should hook my 6 ohm sda-srs up to the 4 ohm or 8 ohm tap. I wonder which is easier on the amp. I think if you hook the 6 ohm load to the 4 ohm tap it is easiest on the amp???
madmax

HBombToo

Originally posted by Jstas
When I turned it on, the right side speaker made a snap sound and then the far right tubed glowed a bright blue. Not good. It could be one of two things.

It sounds to me the tube lost vacuum... if its glowing blue this tells me that that the internal pressure of the tube is at 1 atmosphere. Logic only here, ~ 80% of our atmosphere is nitrogen which when ionized glows blue from recombination of the plasma.

When we say vacuum that means no nitrogen/oxygen in the tube and by hearing a POP/snap that tells me loss of seal somewhere in the tube. The best thing to do is swap the tube and ensure proper warm up.

If you have the schematic I think I might be able to find and recommend replacements. Sorry to hear about a failure but its all part of the tube thing....

HBomb

Jstas

I already have replacements coming.

HBombToo

what type replacement?

Jstas

Same tube that came with the amp. Antique Electronic Supply has hundreds of different tubes in stock. I just grabbed them from those guys. At 6 bucks a piece for the 11BM8's, I'm not going to complain. When I get some cash and more time (work is running me ragged right now) I'll worry about finding better tubes. I grabbed 4 replacements so incase another one pops, I'll be able to swap it out real quick.

Besides, I have to believe that they are of adequate quality. This amp is crystal clear while using them so they can't be all that bad. Tubes are fragile things anyway. Just looking at them funny can cause a filament to snap. I'm not too upset. If its a resistor or something, I put it together myself, I can certainly fix it myself. Part of the beauty of DIY stuff.

What really sucks is, that EQ probably showed up todey and I won't get to play with it until the replacement tubes arrive, hopefully tomorrow.

HBombToo

I took a quick look at the site and could not get the schematic. Did you receive it when you purchased the 502? I would like to look at the filament circuit because if I understand this correctly the filament voltage across should be 11 V with an 11BM8. Probably not the reason for the failure but interesting to say the least.

HBomb

Jstas

The schematic is at home but I don't think it is that detailed.

HBombToo

if you think about it or care to... take it to work tomorrow so you can fax it to me. my work email is hnavaroli@alamosapcs.com.

HBomb

Jstas

Didn't get the replacement tubes yet but I did determine that it was the tube that went south. I swapped the good tubes from the left channel to the right channel and the right channel lit up and played strong. So that one tube that went bad USED to be the only one I had to replace. Dummy me though, I was swapping the 2 good tubes back to the left channel and the 3rd good tube that was in the right channel rolled off the table and hit the floor. Didn't break then. The carpeting broke its fall well. When it did break, it ended up getting stuck in the bottom of my foot after I took a step back to see where it went and stepped on the tube. It shattered and the plate stabbed me just infront of the ball of my heel. Hurts like an SOB today but thankfully I didn't have to pull broken glass out of my foot or do any major damage. The doctor said not to worry about it, bandaged my foot with some gauze and told me to keep it clean for a couple days.

Just call me the dumb gimper now!

I'm glad I ordered 4 tubes instead of 1 replacement!

I was running that new EQ I posted higher up in the thread. Its really nice! Very clean signal and super sensitive! It did exactly what I had hoped it would and that was boost the bottom end of the frequency response. I thought the KLH's sounded great with just the CD player. Then I got the pre-amp and they sounded better and now with that EQ, "shining" isn't a strong enough word! Absitively, posolutly tecspacular would be better I think! Hell, for the 450 bucks total it took me to assemble it, I'd be hard pressed to find something even twice as expensive that sounds this good!



Oh, HbombToo, I have the schematic with me. It doesn't list voltage on it. Like I said, it wasn't too detailed. I don't think it was meant to show the circuit design, just a technical reference for construction. If you still want it, I can fax it over but I won't be able to do it until tomorrow at the earliest. All hell is breaking loose here today and I'm taking the 5 minutes or so that I have to wait for the network guy to get finished patching in the network ports I need to post this. I'll have more time tomorrow hopefully.

madmax

Tubes are a dangerous sport!
madmax

Jstas

Replacement tubes came in. They are Westinghouse tubes. Still Made in Japan. They look a tad different from the other two tubes. I may pull the other two and use the other two Westinghouse tubes so they all match. Then keep the other two as spares.

Anyway, I think I'm finally done piecing this system together. It was just the tube that blew. It sounds really good, I am very pleased and still impressed with the performance of this amplifier. I threw some decent used components at it and it only got better! I was skeptical about its ability to reproduced the rated range for 20Hz - 20kHz. I think it was only because the pre-amp was not putting out a strong enough signal below 1000Hz. I ran the pre-amp out through the EQ and then to the amp. I ran the EQ sliders for everything below 1000Hz, up progressivly on each channel and the bass response came alive! For 30+ year old paper cone speakers, they can kick pretty hard!

So anyway, the original idea was to review this amp. I can say that I would recommend this amplifier to anyone! Its simple to assemble and because it is a simple design, its clean and stable. It can be made to be very attractive looking with a little patience and novice woodworking abilities. While it is down on power compared to other entry level tube amps, it's price level more than makes up for it. For an investment of only 140 dollars for the amp and maybe 50 dollars more in extra parts to build a case for it, one would be hard pressed to find a stereo tube amplifier that is this clean for less than 200 dollars. It is an excellent entry level amplifier, it is a good project to learn with and it will even impress a seasoned veteran. I'd recommend it to anyone. It certainly is a diamond in the rough!

HBombToo

I'm back in the HBomb hole again tomorrow, Thank God!, and back to normal.

If you still want to fax me the schematic I would love to see it. Also, after looking at it I'm actually thinking about buying this little dog. Like you said well worth the coin at 140 plus tube availability is there. After I get it together and figure out the circuit I'll start re-engineering it and should prove alot of fun.

Lets tie off tomorrow.

Thanks
Henry

Jstas

HBombToo, did you get the faxed schematic? If not, I'll try it again Monday. Just let me know. I had sent 7 pages including the cover page. I got an error back on the return sheet that finally came through. I don't know if you got the whole document. There should be the schematic, 4 pages of directions and parts lists and the layout diagram for mounting it on the board. Basically, everything that came with the kit.

HBombToo

No Bud I did not. I also sent you mail.

We'll try again tomorrow.

Henry

HBombToo

After briefly looking at the circuit diagram of the amp, I noticed 1 thing that should be done to extend tube life.

The filament ratings of the tube is 11.2V @ .45 Amps and the Transformer is a 12 Volt jobbie which can be knocked down a bit. Put a resistance in line with Pin4 to Sa1 which is about 1/2 Ohm and can handle something less than 2 Watts.

http://www.tokenonline.net/resistor/carbon-resistor.htm

Remember you add the power ratings of the resistors as they are stacked in parallel for total power in the circuit. The actual power needed taken care of is 1.5W so wahts a 1/2 watt between friends.

HBomb

Look what I just found!

http://s5electronics.com/gpage1.html

They even state 4 or 8 Ohm load is OK! I'm still looking for a replacement transformer that has a 2kOhm primary with a 4/8/16 Ohm secondary. Looks like from the specs the plate resistance is 20k.

Tour2ma

Henry,
Another tubie chimes in big time. That's one thing I've noticed on my road to tubes... everybody tweaks tube amps sooner or later.

Jstas,
Glad to see your little gem is still pleasing and that you did not suffer any damage from your mis-step (reminds me of the time I tried to kick-save a wine glass on its way to a ceramic tile floor --- not a good idea in bare feet).

gidrah,
If you're still around, I don't think I caught what kind of tube rig you're running. I just took the ST-70 plunge myself.

gidrah

My tube rig is currently a ST-70 bi-wiring Monitor Bronze 2 bookshelfs, AMC 1100 pre-amp & Sony PS for CD. Definately nothing fancy.

I'm gonna be tearing down this rig pretty soon for an impending move. When I fire it back up I'll be using a Phillips CDR/RW and try some 8" full rangers on open baffles.

HBombToo

Originally posted by Tour2ma
Henry,
Another tubie chimes in big time. That's one thing I've noticed on my road to tubes... everybody tweaks tube amps sooner or later.

Jstas,
(reminds me of the time I tried to kick-save a wine glass on its way to a ceramic tile floor --- not a good idea in bare feet).

I'm trying to get there before you have a table available. My plan is to use the antique model to drive a pair of 6L6's. I really want to be able to enjoy some of my own DIY stuff. I'm not very crafty and I hope I can get through this.



HBomb I have been there with the kick-save.