Grand 300

[Hellhammer]

Got hold of an old eastern European poweramp named Audio Elektronica Grand 300. The back says 300W into 4ohms, can't confirm this. The output tubes are eight 6P44S and the double triode is a 6N6P. Its working except for one output tube and they are not very well matched either. I have new ones coming. Drew up schematics of it (May have some errors apart from the unknown components):

[IMG:799:300]http://i94.photobucket.com/albums/l96/s ... 0Schem.gif[/img]

[IMG:800:520]http://i94.photobucket.com/albums/l96/s ... d300PS.gif[/img]


The 6P44S should be close or identical to EL500/504. Anyone have any experience using them in audio circuits? Is 575v on the plates safe? How hot can i bias them?

The first filter caps in the B+ rail is a total of 400uF and the second filter in the bias supply is 2000uF... pretty hefty?! Any disadvantages with this? It's going to be used as a bass amp.

I will build a preamp for it. What kind of stage would you guys put as the last stage in the pre-amp?

Thank you!

[tubeswell]

Russians seem to be fond of tetrodes. I can't find any datasheet for 6P44S, but this link suggests they are similar to a 6P45S

http://electronic-schematic-diagram.blo ... 6p45s.html

and those are 'easier' to find data on

http://www.russiantubes.com/prop.php?t=12&p=276

or

http://www.rutubes.com/datasheets/6p45s.djvu

(for which you may need a DjVu browser plugin for windows from here:

http://www.lizardtech.com/download/)

[Hellhammer]

Thank you! Unfortunately the datasheets are only for their designed use not audio circuits (I think, can't read russian). I guess I'll have to trust the designer of the amp that 575v is safe. And I'll bias them pretty cool first just to be safe. An EL504 is rated at 24W max anode and screen dissipation. I measured the screens and they draw almost nothing in idle. So maybe 15W or even less to start with. They are biased between 8-14W now.

So any comments on the filtering? They date from 83-90 so I'm going to do a recap. I can find 680uF caps for relatively cheap. I'm not used to this high filtering though? And the bias cap of 2000uF, is that what I should get?? What do you think?

[Hellhammer]

Oh yes, forgot to ask. Looking at the PS the centertap of the HT winding is connected between the two reservoir caps and the bridge rectifier is referenced to ground. Can someone explain this?

It seems the Marshall Majors were constructed the same way:

http://www.drtube.com/schematics/marshall/200w.gif

[DonMoose]

Oh yes, forgot to ask. Looking at the PS the centertap of the HT winding is connected between the two reservoir caps and the bridge rectifier is referenced to ground. Can someone explain this?

It seems the Marshall Majors were constructed the same way:

http://www.drtube.com/schematics/marshall/200w.gif

That's a voltage doubler.

[martin manning]

Oh yes, forgot to ask. Looking at the PS the centertap of the HT winding is connected between the two reservoir caps and the bridge rectifier is referenced to ground. Can someone explain this? It seems the Marshall Majors were constructed the same way: http://www.drtube.com/schematics/marshall/200w.gif

That's a voltage doubler.

Actually, not. It's a full-wave bridge (in the case of the Major, two bridges in parallel to share the current). The center tap of the HT is cleverly used to make sure that the voltage is split equally between the series-connected reservoir caps.

[Hellhammer]

Actually, not. It's a full-wave bridge (in the case of the Major, two bridges in parallel to share the current). The center tap of the HT is cleverly used to make sure that the voltage is split equally between the series-connected reservoir caps.

Yes I can see how that would work. The bleeder resistors should already divide the voltage equally though?

Any thought on the filtering? Should I go with close to original values?

Thanks for your input guys!

[swordbreaker]

Hi guys, Hi Hellhammer,

sorry to reopen the discussion in thread but I didn´t really found anything in the web (except some bulgarian and russian sites) about this amp.

I catched two of these at ebay for a "ok" price and wanted to ask now about your experience with this kind of amp. They aren´t still delivered but I already watched out for matched quartetts of 6p44s.

For which purpose do you use this poweramp? Only Bass or also for guitar?
Which kind of preamp do you use (tube preamp with 12ax7 or something else like boss or line6 stompers)?

How do you like the sound/sound quality? Anything I have to take care of?

Would be absolutely grateful for any kind of information about these poweramps.

Greets

[Hellhammer]

Welcome! That's cool you found two of these. I wish I could tell you anything about the soundquality but mine needs new caps before I comment on that. It's still under my bed waiting for some love. I actually have the caps I need at home so maybe I'll have to dig it out.

I just briefly compared it to a 200W hiwatt power-amp (4xkt88) using a proto tube-preamp and it sounded really bad in comparison and nowhere near 300W or 200W for that matter.

Well I measured b+ on the first cap and saw it drop to zero in a second after switching off, so i'm pretty sure it desperately needs new caps. I'm sure it will be a BIG improvement. That said I'm not too sure about 300W at lower frequenzies as the trannys are about the same size or smaller than on the Hiwatt.

Oh and a warning! The wires to the topcaps have no insulation, the top caps are actually just simple clamps soldered to a thick bare wire, so keep your hands out if you don't know what you're doing. 575VDC is exposed as soon as you take the back cover off... it bites hard and might kill you!

Please post pictures for future reference. I'll post some when I get it out.

[swordbreaker]

Hi Hellhammer,

I didn´t really expected any kind of reply so I am glad for your response.

Yeah, I share your assumption with the caps if these thingies are probably older than 25 years than something more actual from nichicon or panasonic would be nice in there., I fixed so many electrical stuff by changing almost or at all leaking caps. Would be cool to have a audio sample from a working one to have a rough comparison when fixing mine.


I have to admit that these are my first tube amps and I would like to dig deeper into this topic since I love the sound from a tube amp and especially from vintage stuff. It´s simply without comparison. I also want be ready enough to assemble a kit from e.g. weber amps including biasing and troubleshooting so I am not dependent from service shops and wankers waiting to pull as much money as possible.

Hm, you say the trannies are too small for the displayed output wattage? Maybe it´s possible to do an upgrade, maybe oversize them as much as possible. But I´ve got firstly get familiar with those beasts, currently I am still on information-collect-tour.

Already noticed on the pictures the not-insulated wires, gotta replace this with a more modern solution. Russians are brave, so I don´t wonder myself about that.

Here are some links I´ve found about these amps:
(I used google translate, works excellent!)

http://www.ljudbojen.com/viewtopic.php?f=24&t=57751 (there is schematic in one of the last posts, maybe we should get in touch with these guys?)
http://www.diyaudio.org.ua/viewtopic.php?f=43&t=2583 (guess he wanted to sale it, nice pictures, should save them down to disk)
http://forum.guitarplayer.ru/index.php?topic=216883.0 (nice cat ^^ discussion seems idiotic, at the end they talk about cr*p)

Greets

[Hellhammer]

The first link is my thread on a swedish forum. That schematic I found on a polish forum. I later redrew the schematic reverse engineering my amp and it differs a little if my memory serves me correctly. I'll have to take a closer look at my amp and the schematics when I have time. Too much to do, not enough time.

[swordbreaker]

Oh... damn, I didn´t looked properly.. It´s of course the same username *lol*

I will try to complete the schematics as soon the amps are on my table.

[swordbreaker]

Finally the amps arrived and I dont know what to say: they sound bad (in a positiv manner ) like something big sleeping in there waiting to be released. We had a boss gt-100 laying around in the rehearsal room to raise the guitar to line level and a 300w bass box with the needed impedance and it was OK (but I dont like that modeling stuff, got to get a nice pre with 2 or 3 tubes like these amt ss series)

Now the not so good news:

Both amps need fresh tubes and need to be biased (got a lot of 16x NOS 6P44S for 60 dollars from moldawia ), microphony is clearly hearable.. some of the tube´s are simply worn and through.
One amp hums from the right tranny, got to check everything, maybe it´s not a big problem and it´s somehow loose because of transport or self-repair attempts. Maybe need a new one.

Like you I simply need some time for checking. Both amps have crackling volume pots, maybe I will search for some nice alps pots to replace the old ones.

Since I am currently short on time I cannot put some pics on with a sound sample but I promise some content within the next two weeks when we moved to our new house in the beginning of February.

Man, I am so glad that I found these things and guess we will have much fun with these. My goal is to put some stuff on youtube, maybe we can find someone else playing on these heads.

Best Greets and a nice weekend

[swordbreaker]

Hi, just wanted to give a small update.

Due to no time to repair the amps by myself, I decided to take em to a well known repair shop in my region with excellent service around tube gear and Hi-Fi Stuff.

I took the amps to him and he told me like everything will be ok, following a talk about amplifiers and life itself.

Previously I thought there would be a cap replacement necessary, but I was lucky enough due to the fact that the caps werent used not even a hundred of hours according to his measuerements.

Due to their military grade (including all the other electrical parts) the amp should have a long lifespan also when used regularly.
I have had a small shock after getting the email with the invoice before getting the amps, since he wrote "no parts were changed". Already hearing the muddy but loud output in my inner ear I was a bit afraid about the results of the repair.

I told myself "Alright, be brave and trust the impression which you got by his self built 1000 watt tube" and went home with the amps in my backpack. Grabbed also some new cables with nice electrical properties on my travel - just in case.

Somewhere in the night - had the house for myself - I popped a cold beer and grabbed my guitar.

Unfortunately I had some stomps before my preamp (damage control demonizer with tad premium - lower gain - TS9 - Fuzzfactory - Boss Delay) and it sounded somewhere strange.

Then I cleared the pathway between guitar and preamp and reduced the gain on the demonizer.

MY GOSH!

You know how a fender superbass sounds? Just imagine only the big fat power amp section with 300+Watts tube power. Thats really a lot and very raw.

According to the measurements of the tube doctor, the amp produces 338watt SINUS output!

The strings of the guitar have all their own space to emit sound (10-46 ernie ball) and it´s incredible how powerful this amp sounds but not with a certain sound charakter. You hear clearly the sound shape of the preamp and I like such properties since it allows to try different preamps which are not "aftercolored" that much by a tube poweramp.
It simply sounds warm and "tubish" with slight rounds in all frequencies which turns him into a blazing beast with straight and clear voice. Very Versatile!

Here in my room s a jet city 4Ohm/300Watt box (not probably the best speakers but ok) and a custom made bass box with one big fat speaker which has 4Ohm/500Watts output.

No matter if bass or guitar, both sounds terrific, incredible and when turning the volume knob of the poweramp to 3 o,clock it gets into ear-splitting and very dangerously loud volumes, but still very dynamical and clear.

The tech also told me the frequency range, which goes from (surely unhearable) 14Hz to nearly 70Khz /-3db and fits also to a HiFi-Grade Amp. I was hinted to listen to some music over both amps. Due to no availability of some decent hifi speakers I was still not blessed with that experience.

Currently I try to record some examples in a good environment without reflections and good for some loud rehearsal.

Hey, if you don´t need your amp, I will buy it.
I guess I will buy every of these kind since they are pure and nice tube power amp with lots of potential for different kind of uses/instruments due to their sweet unlimited headroom and nice afterglow from the tubes.

My bassist tried a cheap dimavery bass over a old 70s guitar amp preamp section with a separate output from the solidstate preamp into the russian tube power amp. It sounded incredible, so clear but with two different kinds of charakters due to the different amp "souls". There were moments when he started to play some parts of primus and the slaps sounded great, even with the cheapo bass.

I will try to acquire also some other preamps like the tube beta hybrid from correct sound custom or a soldano x88 clone. I would have a peavey tubefex here but it´s unfortunately broken (fried PCB).

Please give this amp a chance because it´s really great!

Greets

[Structo]

Wow, back from the dead.

Glad you like it!