Rocky - The Quatroquel

little eddy · Post by **little eddy** » Sat Mar 14, 2009 12:25 pm

Seeing Cressy's comments regarding the EL37, might these be any good?

http://cgi.ebay.co.uk/EL37-MULLARD-Tube ... dZViewItem

cressy · Post by **cressy** » Sat Mar 14, 2009 1:11 pm

they appear to have a top cap so abit of modding would be required if they do, last pair i saw went for about 60 quid, these were the fat bottle ones with the brown base. they dont look like el37s to me tbh! but i cant read the italian description

little eddy · Post by **little eddy** » Sat Mar 14, 2009 2:25 pm

Yes I was a bit sceptical about them.

Look more like an EL34 envelope. Although I'm not the most knowledgable, I've also never seeen red writing on the few Mullard valves before.

Tried translating in Bable Fish. Says something like "Is super heads"?

Cressy Snr · Post by **Cressy Snr** » Sat Mar 14, 2009 2:28 pm

Hi Eddy

Those are NOT EL37s

Real EL37s are ST shaped.
There are Fat bottle ST shapes, which are supposedly the best
and then the thinner bottle ones, shaped exactly like a GZ37 rectifier.

Don't touch them with a bargepole.

Steve

Mike H · Post by **Mike H** » Sat Mar 14, 2009 4:46 pm

Mullard data sheet:
http://frank.pocnet.net/sheetsE2.html

... says nuffink about no top connectors. Plus they're "Amperex", not Mullard

little eddy · Post by **little eddy** » Sat Mar 14, 2009 4:48 pm

Well I couldn't wait any longer so with the kids at a party this afternoon I just had to get the Rocky into my system. Couldn't be hastled with getting the vinyl out so started with my CD and AN DAC.

In terms of the performance of the amp, I was/am astounded. I've spent a tad over £300 on bits, probably far less than the cost of the upgraded components on my WAD KT88 PP and although it sounds different, in terms of overall quality it is at least a match. My only problem now is that I don't know whether any minus points are due to my amp, or the fact that this is really the first SET amp I have listened to. May be worth listening to Rocky for a while and then put the WAD back in for a comparison.

Bass and midband seem more musical but doesn't quite have the same top end clarity/sparkle (or maybe that was harshness). Saying that, there are definitely nuances and details that I have never before registered and the soundstage is wide and continuous with depth.

In terms of the power and sensitivity of the Zingalis. Again it's slightly confusing because although they obviously won't go as loud, I wonder if this is because the overall sound is more 'relaxing' and I just want to turn them up more than with the WAD.

After a couple of hours listening, still thinking that it lacked a little sparkle, I had a play around with the interconnects. I was using some pure silver ones so exchnaged them for copper. Definitely a quantum shift in balance with the top end now more pronounced. I have lost something slightly in terms of the soundstage and it may now be slightly harsh but at least for the moment seems a tad more balanced. I did however notice myself turning the volume down a bit so you never know, I may have gone a bit too far and may resort back to the silver ones after a while.

So I'm like a dog with two d****. back to more listening and smiling like the preverbial Cheshire cat. Might get some records out tonight to really understand how far I've progressed.

One thing's for certain, I feel confident enough to have the amp critically reviewed by you 'experts' at the next meet if I can make it.

Mike H · Post by **Mike H** » Sat Mar 14, 2009 4:51 pm

Most prob'ly what they should look like ~
https://www.tubeworld.com/el37.htm

Although Amperex versions is mentioned

cressy · Post by **cressy** » Sat Mar 14, 2009 5:16 pm

one good thing about these is that theres alot of other valves that will go in it, at the mo ive got some colmor 6l6s in mine that are lovely, ive also got some 5881s and kt77s so if you want to have a play i'll send them on for you to try, also got some golden dragon 6sl7s if you want to try them, (if your using 6sl7s as drivers of course)

little eddy · Post by **little eddy** » Sat Mar 14, 2009 5:26 pm

I've not tried the Mullard GZ34 yet but with the limited number of options I have, I've currently got installed a pair of Toppsy's RCA 6SN7s and the Jan 6L6s I bought of you.

cressy · Post by **cressy** » Sat Mar 14, 2009 5:58 pm

i did find those particular 6l6s a little harsh at the top end so it will be better with some others in, the colmor ones im using have a much bigger envelope and do sound better to my ears, i found that different drivers seem to make more of a difference to the top and different power valves more to the bass/lower mid. dunno why. im using some sylvania 6sl7 gt's as drivers and these seem to make a good combination. with mine the rectifier didnt seem to ake alot of difference to the sound, tried a mullard gz 34, jj gz34 a mesa boogie 5u4g (i think) and a sovtek 5ar4. and the difference was more of a personal preference. i just stuck in the cheapest tbh so if it blows it doesnt matter!

little eddy · Post by **little eddy** » Sat Mar 28, 2009 4:15 pm

ROCKY GOES DC

I've been playing around with the amp these last couple of weeks, the first part of which was tinkering with settings of the SRPP input stage. With my initial 1.5k resistors, the current was quite low at 3.6mA and grid bias of 5.6V. My previous notes were at these settings but under the guideance of the ever helpful Nick I aimed to increase the current to circa 8mA. I managed to get to 7.5mA by fitting 470R ones and decreasing the value of the resistor in the power supply RC network to compensate for the larger volt drop, getting the supply back to the original 300V. What a difference. Initially my thoughts were that Rocky now sounded thin and lean but my impression changes with further listening, with the amp now being more transparent and authoritive. The previous set up in retrospect was bloated and artificially euphonic although it did really get my foot tapping. I am amazed with the scale of changes possible by just playing around with the current and bias.

Today however has seen another quantum shift and I feel it is for the better. As on the DC Heater thread, I fitted the previously bench-tested LM338 regulated supply and the changes are far from subtle. Yes as most people before me have reported, the bass seems to be more controlled but in my instance, the amp now seems to have stepped up a gear in terms of the degree of detail now eminating from my speakers. This seems especially so in the upper registers with percussion detail particularly being more recognisable and the amp generally sounding slightly sharper.

The one thing that the DC mod didn't stop was a small hum that I thought it might, particularly on the left channel so this must be coming from elsewhere. It actually now if anything is slightly more pronounced! It's not distracting but I just want to find the source.

Well it's back to listening for the next two days until Tuesday night when I'm off to have a listen with Toppsy, and perhaps a play with some Mullard 6SN7s and some different decoupling caps.

I have attached a photo. Things are now fairly tight and I'm worrying whether I'll have room to try SS regulation of the SRPP HT supply.

Mike H · Post by **Mike H** » Sat Mar 28, 2009 11:49 pm

Interesting about the hum ~ what's that small TX next to the matrix board? I presume it's a mains, and the big black TX in the background is the left channel output? Could be therefore the little TX is coupling to the big TX.

little eddy · Post by **little eddy** » Sun Mar 29, 2009 10:20 am

Mike,

The blue one as you rightly guess is the the left output TX, the small one being a 12VA one to power the DC heaters (and yes with hindsight probably under-rated). The TX is closish to the output TX as you can see from the picture. I was trying to keep the 240V/9V input/output wiring away from the output TX, and being fitted first, I made sure I left plenty of room for the DC supply board.

The hum is interesting. Before I did the DC mod, although quite low, the hum was more distinctive, I would have thought predominantly/solely 100Hz. But since the change it is slightly 'muffled i.e. not so much a single frequency, and with your comments, maybe this is a small amount of 50Hz induced from the small DC power TX?

Your logic may therefore be correct and now that I've got the whole thing fitted, next time I'm inside, I'll try to inch the TX towards the DC board and I should get another 10 or 15mm gap.

When looking at the picture it occurs to me how close the TX is to the 0V busbar but with the hum being more noticeable on one channel I do not see this as much a concern. I also notice that I didn't bond the TX to ground but I guess it's not on the outside of the enclosure!

If my memory serves me correctly (and I'm talking about 25 years), doesn't field strength decrease as a square of the distance?

Post by **Nick** » Sun Mar 29, 2009 10:37 am

Try rotating the TX, if its induced, then the level will change. It may be that because the TX is being pussed it might be saturating and throwing more field because of that.

Mike H · Post by **Mike H** » Sun Mar 29, 2009 12:39 pm

Oh beg their pardon, they're blue

Also, maybe a largish aluminium plate in between them, and grounded to 0V. Might help as well.

That's a point, are the mountings of the TX's actually grounded? Cos they're just screwed onto wood?

audio-talk

Rocky - The Quatroquel

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