6V6 EH-150

[David Root]

It sounds good thru the Celestions but a bit less hum, and the scratchy pot.

The old P12Ns out of '50s and '60s organs are reasonably priced compared to the ones Leo used, because they don't have the bell or the blue Jensen sticker. I bought a pair off Ebay a couple years ago for $170. The Alnico 5 in them alone is worth more than that today! They also almost always have the original cones too.

AFAIK those organ pulls are the same as Fender's, same voice coil, same cone. They sound great. Another great old speaker for this amp is the Altec 417. I have a pair of 16 ohm 417B in a 2x12 that I'm going to refresh my memory on today.

My PS droppers are a 10K 2W metal oxide and a 43K 1/2W carbon comp.

Anticipating a bad V1 6SQ7GT, y'day I bought two NOS NIB Tungsols from an Ebay seller that I have bought quite a few good tubes from in the past. Man are prices nuts now! $30 each! I didn't think I'd have to spend that much but just about all else on Ebay looked very tatty and much of it not a lot cheaper and not NOS. The good looking stuff was insanely priced. "Matched" quad RCA for $200!!

[Smokebreak]

Ok thanks for the info. I'm trolling ebay waiting for an organ pull to pop up with seller unaware of 220 code, but that doesn't seem to happen these days

Concerning the lack of screen resistors I have, how did you come to 1K as a suitable value? I was reading in the other current thread about them, and I've always thought about them as being fairly arbitrary in terms of value, to a point, but i see this isn't the case? I'm assuming I'll need to check my bias again too if I implement them.

I know Fenders ran screen voltage higher than Vp, so is tube life the primary concern here?

Also, if I have no oscillations or blocking distorion, and dig the tone, would it still be a good idea to put in some control grid resistors as well? 1.5K?

Thanks, J

[David Root]

Screen gridstoppers about 470r and below just help prevent parasitic oscillations. With 6L6 and 12AX7 this is not a real big deal, but Fender did as you know go to 470r from none back in the later tweed days anyway.

In hifi circuits that can use high gain high conductance low Rp pre and driver tubes, like the D3A, you will always see gridstoppers, and even platestoppers on big output tubes, because high Gm tubes are prone to parasitics. EL34s and EL84s are relatively high Gm tubes too, not to mention EL37.

Above 470 you start to get tonal effects, compression, and some protection against screen current surges. Most people me included can't tell at 1K but at 3k3 or 5k1 like Dumble used a lot, there is a noticeable effect. But there is also the real protection against screen current overload too, so with EL34s and I would say any valuable old 6L6s or other NOS/UOS power tubes it's worthwhile.
For example I have a pair of NOS NIB EL37s that I will try in my EH150 now that I have changed the power supply to 280V B+ and choke feed. Choke feed lowers the inrush peaking over cap feed plus I took 100V off the B+, so I feel OK with the 470r screens I have on those expensive tubes.

I'm also using 1k5 on the 6L6 grids. Leo used them and he would not have gone to the added cost without a good reason ie anti-parasitics. How do you know you don't have any parasitics? Have you put your amp on a scope? If not, you don't really know if you have parasitics or not. They can rob power way above audio frequencies and also do all kinds of resonant nasties that your tubes don't like.

Yes the old Fenders and many others also ran screens above plates but it mucks up the tone as well as taxing the screen. Im probably being overly picky as I only have 1V over plate voltage, but that's just me.

[Smokebreak]

That's good info! I always overlook the oscillation issue. I always crank everything, and if I can't hear any strangeness, I assume there is none, but that's obviously not the way it works. I have a heathkit scope someone gave me very recently, but honestly, I find it quite intimidating, as I know next to nothing about how to use it. I may lean on you guys soon to help with that. I'm about to fireup another express, so it will probably be the perfect time

I got my Chinese 6G2Ps today and they sound about 10X better than the metal 6SQ7s. Most of the weird noises are gone too. I installed 1K 3W screen resistors, and now plates are 315, screens 320, as opposed to my previous 320/330. I'll try 1.5K, as I couldn't hear a tone difference w/ 1K.
I've been trying out some speakers I have here and the wrong speaker definitely makes the bottom end go splat.
Rk is 300r, 22V, 36mA, so I'll go a little hotter here, too.

[David Root]

I've had a scope for several years, and the manual, and I still can't figure out how to get it to work properly. I need scope 101 course.

6G2P vs metal 6SQ7. Sometimes those old metal tubes will sound better than a -GT glass tube, sometimes not.

An old guy (mid -80s ten years ago) who had the only tube shop in Salt Lake when I lived there sold metal tubes cheaper than the glass equivalent, and didn't recommend them. He said they will eventually overheat and fail. He was old enough to be working when metal tubes first came out, so I'm inclined to believe what he said. OTOH he didn't say they sound worse than the glass equivalent.

What speakers did you try and which one(s) gave splatty bass? That would be very interesting to know. These amps weren't designed for permanent magnet speakers, as you know, neither alnico or ferrite, but they sure do sound good with alnico. I never tried anything but alnico in them, but there is probably a good ferrite magnet speaker that will sound good, maybe an EV12L or an Altec Type II? I just figured an old original cone P12N is probably as good as anything. Since you're using 6V6s why not try a Celestion G12 Blue? OTOH the EV or the Altec are so efficient your 6V6s will sound like a pair of KT88s!

At 315Vp and 36mA you're getting close. I forget what the max. screen Pd on a 6V6 is but I don't think I'd push them much past 40mA. Depends how tough your 6V6s are! I recall a very clever dude on diyaudio whose avatar slogan is "crank them up until they explode, then back 'em off a bit".

You can push the old 6V6GTAs harder than the GTs, and probably the GTBs too.

[Smokebreak]

Well, I've only started learning about and experiencing different kinds of speakers over the last year since this amp building started. I'm pretty cheap too, so apart from all the stock stuff in my Fenders, I don't really have many nice speakers. Right now I've got a homemade 12" cab that has one of the "designed for fender" speakers in it. I think it's what they stock in the blues Deville, etc. $20 on CL and that's what sits under my bench for amp testing . That's the one that sounded splatty with this amp. My other cab is one of those cheapo seismic cabs with a vintage 30 and a G12T75 That setup sounds pretty good, with the latter beating out the V30 for this amp. I've tried the Weber sigs, and didn't care for them, along with the Legends, which I guess are what they vaguely claim to be the "original" scumbacks, and sold them within a week. I do have some blues stock in an ac30 that I'm trying to sell, so I may rig that up to this amp to get some more perspective.
My favorite speaker I have is an SLM Electronics 8" that is stock in a Caliphone "Music Monitor" that I rescued and built a SE bad cat thing in, and it's super crunchy and gnarly but tight! I always end up playing the " Stay with me " riff for 10 minutes when I play that amp.
So, for this EH-150, I've commissioned a combo cab build, my first, so I really wanna get the speaker right. I'm leaning towards a P12, if for no other reason, just to see what they sound like on the other hand, since I just have the 6V6 version, I'm also considering a more efficient speaker, for cleans. See, I get lost in speaker land.
As far as the bias, when you say "screen Pd" do you mean screen and plate dissipation? I'm showing around 9W dissipation so I figured I could go up to 12 or even 14 with jjs . I'm looking at this datasheet : http://www.r-type.org/pdfs/6v6gt.pdf
I've been looking at the class AB section, but the numbers you're talking about , in terms of getting close, seem to fall in line with class A, but I'm not convinced I'm running class A. Can you explain what I need to be looking at here? Of course we know the max Va is a lie

[Hepcat]

the speaker in a Charlie Christian era EH-150 was very likely a field coil speaker. My experience with them (in a late 40s Leslie and a couple of old amps) has been that they lack any real bass and have less magnetic field than a PM speaker. If you don't like the Weber speakers, then a vintage P12R won't likely float your boat either. A British speaker could be your best bet in a 12. (I prefer them also)

[Smokebreak]

Thanks man, I have been diggin on the celestions lately.

[rp]

I want to follow up here, as I'm completely blown away by this amp.

If you're willing to 'play outside the box' these amps from the neolithic are a gold mine of tones. They distort in the most unique ways, and the cleans are immediate, warm and rich. if you're fixed on getting classic tones you might not be happy, but tone is just what you make of it, you will it into existence. Primitive octal amps are more fun than pedals.