FreeWilly
392 posts
Jan 14, 2014
9:29 AM
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Hi guys,
Sorry if I'm just being the guy that's new to gear and tries to wrap his personal questions in so-called issues of general interest, but... I thought this might be an issue of general interest :)
Why is it that there is so much talk about 5751 pre-amp tubes for the VHT special 6 and other amps like champs, EVJ's, while at the same time the best harp amps that size (Marble Max, HG2) use 12AT7 or 12AY7? I even read the AT being called a terrible tone generator by Rick Davis (and supported on this by many others). But the Marble Max sound amazing.. Is it the circuit? I would expect the harpamp builders to take out gain rather than pile it...
I still think my Vht sp6 is too gainy with an 5751 (sounds like a musical but very pissed of wasp, even with C11 and 13 taken out (as suggested by our distinguished forum member 5F6H), the tone all the way down and an ultimate 57 for a mic), and are going to try an ay7 with it (learning by doing). And no, it's not my technique btw :)
Is it the difference between Rock and Blues? Any thoughts?
Perhaps it is a personal question after all. I'm just trying to develop my ears I guess. What do you guys think?
Last Edited by FreeWilly on Jan 14, 2014 9:35 AM
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5F6H
1735 posts
Jan 14, 2014
10:45 AM
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I look at it as a balance, might be a higher mu tube like 12AT7/5751 suits a circuit or mic better, or a 12AY7...or maybe lower, suits another. There's not really any right or wrong (as long as you aren't burning up resistors - not very likely in a low voltage preamp like yours).
I have a 5751 in my modded Champ, I have used that and 12AY7 in other SE amps. 12AT7 doesn't always sound great as an input tube, can often be glassy in amps not set up as a good match, but I do have a couple of amps that sound great with a 12AT7 in V1, these are aimed at a more transparent sound, not crunchy...though other fellers that have tried the same amps with their mics preferred a 12AY7...I was brave & took it on the chin!;-), I know guys who have preferred that tube in V1 of a bassman too (whether I agreed or not).
Rick's quoting an article written by tube amp expert Myles Rose, he's a clever guy and there are some things to think about there, but don't be afraid to try stuff out & see for yourself - tubes make no sound until you put them in a circuit, so there may be rules of thumb, but also combinations & applications that aren't common & need to be experienced.
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Rick Davis
2864 posts
Jan 14, 2014
11:08 AM
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Mark, I first tried a 12AT7 several years ago and thought it sounded as harsh as an icepick in my SF Champ. So I did some research and found the article you reference.
I've tried it a few time since then and my opinion has not changed. So, just as a general rule of thumb, when players ask me about preamp tubes in small amps I tell them 12AT7 = bad and 5751 = good. At least it is a good place to start.
But not all 5751 tubes are created equal. I don't like the JJ 5751 nearly as much as the NOS JAN Philips tube, which I use in some of my amps. That is the specific tube I recommend.
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
Last Edited by Rick Davis on Jan 14, 2014 11:16 AM
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Rick Davis
2865 posts
Jan 14, 2014
11:17 AM
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Freewilly, a VHT6 should not sound like an angry wasp with a 5751 and the tone all the way down. Are you playing too loud in a small acoustically live space? That will make many amps sound ugly even before they reach the point of feedback.
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
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Kingley
3392 posts
Jan 14, 2014
11:23 AM
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I can't comment on a 12AT7 as Iv'e never used one.
Interesting that you find a 5751 too "gainy" in the VHT though. I was playing my VHT for a while after work today using an SM57, volume on about 9 o'clock and tone on 11 0'clock and don't find it "gainy" at all. I was able to vary the tone from clean to dirty just by breath force and cupping technique. I think the 57 and the 545 are a perfect match with the VHT. I'm running a JJ6V6 and a JJ 5751 in mine.
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FreeWilly
393 posts
Jan 14, 2014
12:10 PM
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Thanks for the replies guys.
Perhaps angry wasp is overstated. I can understand what you say, Kingley. The vht is great, and I like what I got for my money. I get a good sound, it will do clean even at 4 o'clock (almost open) and responds to cupping with nice break up. The room was fine. We practice in a big and well isolated space. The vht cuts through the full band. So the upside is there too. I love my amp and sometimes feel like hugging my first real amp (when I'm not touching my ultimate 57 that is :) ). It's nice to finally have some gear and be able to play amped up! I saved up for it long enough.
The sound is just a bit harsh to my ears. I'm just starting in this game, but feel the sound could be better. I was trying to describe the downside. It might be the 5751 I use (Tad premium selected), it might be the speaker (am still waiting for a friend to bring his legend 10516 to try that), and it will have something to do with my tone too, although I haven't heard youtubevids of this amp sounding much better. There's always this slightly harsh sound. Don't you guys think? Perhaps that's the only way to cut throught a mix. But I heard a Marble Max, and that doesn't have this harshness. So that's why I thought: perhaps try the pre-amp tube that uses.
I weighted your opinions, revisited Rick's vid with the 5965 tube (if that's the number) which sounds a bit dull indeed and ordered a 12AT7 (JAN Philips). A NOS 5751 seems to cost a lot more. So I hope the TAD is good. Will report on the findings when it gets here. Someone has to try this right? Vht sp6+AT...
Last Edited by FreeWilly on Jan 14, 2014 12:13 PM
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5F6H
1736 posts
Jan 14, 2014
12:57 PM
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@Rick "Mark, I first tried a 12AT7 several years ago and thought it sounded as harsh as an icepick in my SF Champ. So I did some research and found the article you reference. I've tried it a few time since then and my opinion has not changed. So, just as a general rule of thumb, when players ask me about preamp tubes in small amps I tell them 12AT7 = bad and 5751 = good. At least it is a good place to start."
I would agree in as much that 12AT7 has not, as far as I can recall, ever been my preference in a SE amp that I have tried (I have tried the Maxs with 12AY7 & even subbed in a 12AX7, which I also liked)...5751 is my first call for this kind of amp, gain isn't typically that much different between that & 12AT7, but 5751 has certainly got richer harmonics (a very different plate resistance too). In fairness, I can probably count the models of amp that I like with a 12AT7 on one hand...& I built 3 of them ;-). For the time it takes to suck & see, I'd try it, but I wouldn't recommend spending money on one in a vague hope.
FreeWilly, there's a few other things you can try, you have done a couple of these already. I do not own & never have owned a VHT Special 6 (but never say never...), these suggestions are just that, suggestions:
C8 - 4.7uf is too small, 25uf/25v would be better, no need to go much bigger with a small amp. Observe correct polarity (waisted end to valve pin).
R12 - Bypass with plain wire, this turns off your "treble pot"...which you can't adjust otherwise (whether in clean or boost modes).
R13 - This is the "bass" resistor 33K is quite small a value, I'd look more at 150K to 220K (bass full up).
C11 - remove.
C13 - remove.
Optional/fine tuning:
C15 try removing, this will lower gain at the power tube, if it kills the amp tone, just refit (observing polarity).
R17 - Run a 33K or 47K 1/2W resistor from the valve side of this resistor to the hot speaker jack terminal - this makes a 'negative feedback loop', I normally prefer a loop on SE amps as they can be a bit bitey without. If your amp has a 4/8ohm speaker use a 22K resistor. WARNING: After fitting this loop, your amp may howl as soon as you turn it on, this is because it was built without a loop and OT polarity didn't matter - now you have a loop it does! If you get howling either detach the loop, or switch around the blue & red wires from the output transformer primary, that connect to 6V6 pin 3 & "B+ 1".
R8 - I like 2K to 2.2K 1/2W here to reduce fuzziness with a mic.
R5 - Try larger values to brown off the tone, the bigger you go the less voltage on the preamp valve & grindier the sound, I'd guess at ~47K (2-3W rating) might be around your useful limit?
The footswitchable "clean/boost" is a resistor that almost disconnects the tone stack, perhaps leaving the amp not quite identical to a 5F2A, but along similar lines.
Observe proper safety protocols (with the amp unplugged from wall AC, throwing the standby into "play" mode should drain your caps via R25).
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http://www.facebook.com/markburness
Last Edited by 5F6H on Jan 14, 2014 12:59 PM
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FreeWilly
394 posts
Jan 14, 2014
1:02 PM
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Thanks for the suggestions! I already removed C11 and C13 as you mention. The others involve soldering. A hurdle I might take. If I do, I'll report back!
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Rick Davis
2869 posts
Jan 14, 2014
9:01 PM
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FreeWilly, ya, the price of those NOS JAN Philips 5751 tubes has gone WAY up. When I first started buying them from Tube Depot in Memphis several years ago they were $19.95. Now they are more than twice that.
Did you see this video?
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
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FreeWilly
395 posts
Jan 14, 2014
11:54 PM
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In that vid, the harshness is almost gone! Still. You hear it a bit sometimes. Or you hear it used to be there. In an otherwise almost muddy sound. Would that amp still cut through a mix? Very nice sound nevertheless. Pretty much perfect vintage sound. No two ways about it! Not really what I'm looking for though. Looking for a little more cut, with highs that are not harsh (if that makes sense).
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Kingley
3393 posts
Jan 15, 2014
9:03 AM
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FreeWilly - Do you have an example of an amplified sound you like? Maybe if you provide some examples of sounds you like, the guys that know circuits could give you some ideas on how to make the VHT sound fairly similar to them (if that's at all possible of course).
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rogonzab
454 posts
Jan 15, 2014
9:58 AM
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FreeWilly,
"In that vid, the harshness is almost gone! Still. You hear it a bit sometimes"
Where??
Can you post an audio of you playing whit the amp? that can give severals clues to help you.
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Rick Davis
2874 posts
Jan 15, 2014
10:52 AM
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Freewilly, I'm not sure we are talking about the same thing. Where is the harshness on the video? Give us the time stamp. I'm not understanding what you mean.
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
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htownfess
285 posts
Jan 15, 2014
1:24 PM
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I would remark that besides the issue that Rick and 5F6H talk about, that you probably won't like the result if you drop a 12AT7 into a SE preamp that wasn't specifically designed to use that tube for harp, I ran into an apparent problem with current-production 12AT7s that probably contributes to this tube being harder to like for harp: in my experience, the new ones run significantly different than NOS ones do, enough so that I think most players could distinguish between them in a blind test.
I have an amp with an input stage designed around the 12AT7 and had used NOS 12AT7s in it for at least half a dozen years, but wanted to check current 12AT7s even though the vintage ones are still pretty cheap and plentiful because I'd rather not be dependent on NOS stuff. I believe I got Sovtek, JJ and EH 12AT7s and just stuck the JJ in and went to a jam at a very, very familiar stage without playing the amp first. If it had been food, I would have spit it out, it was that bad. So stiff and sterile that I got the multimeter out as soon as I got home, in case something was wrong with the amp.
The input plate voltage measured way high, like 15% higher than I expected, so I tried the other two new 12AT7s I had around and got a similar result, then found it behaving properly again when I put a vintage 12AT7 in. A given tube type is going to show some variation in plate voltage within different new examples of the same brand/model, let alone different brands, but this was way too much difference. Plate voltage is not necessarily the cause of something the amp does that you like or dislike, but it's definitely an index of how a tube is running, so seeing a big swing like that pushed me to investigate.
I think I had about a dozen NOS 12AT7s because somebody had run a batch deal on mixed US ones, so I just measured all the vintage and current ones I had around. Obviously it wasn't a big sample, but I think I had at least two of the JJs on hand, so it was at least four new ones. The mean and median were pretty close within each of the two groups, and I think it ran about 80-85v for the vintage 12AT7s and 100-105v for the current-production ones, and I think a 10% change in input plate voltage is enough for most players to detect easily, if it's going up or down 10% from something they like and know well.
I bought another JJ and EH, hoping I'd had outliers before, but the new ones ran in the same range. I also got the Tung-Sol RI 12AT7 whenever those came out, and there was a burst of very bad language when I measured it because the T-S reissues have been pretty good tubes for me but their 12AT7 did exactly what the other current ATs I've checked have done.
I admit that I have not taken that same amp and changed the circuit to get the plate voltage into the desired range with new 12AT7s, because I haven't had the empirical patience/time to do that so long as NOS 12AT7s don't cost much, and because adapting it for new production would make NOS run wrong in there. I suspect new 12AT7s would be okay if I dialed their plate voltage down in there, but we shouldn't have to do that. An amp designed around new 12AT7 should be fine with them.
I did have the patience at the time to check 12AX7, 5751, 12AY7, and 12AU7 for the same problem, new vs. old, and the problem did not show up with the examples I had around of all those. Even the Sovtek 5751, which I expected to run high because those have been so bad for harp in my experience, tracked close to the NOS ones I had, which illustrates what I meant about the plate voltage sometimes being more of a symptom of what you don't like rather than the cause of it.
I believe some tube dealers/mavens advise using only NOS 12AT7 as BF Fender tremolo tubes, saying only NOS lasts well there, indicating they know something's up with new ATs. Guitarists often want clean for Fender phase inverters, so the new 12AT7s may not bother them sonically there. But for harp purposes, I have found the new and old 12AT7s to be different tubes, just about, and avoiding both may be simplest. YMMV.
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FreeWilly
396 posts
Jan 16, 2014
7:28 AM
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Hey guys,
Very informative, htownfess. Thanks for sharing.
Thanks Kingley. Your question made me think about what sound I look for. Interesting! And kinda dumb I didn't think about it yet..
The answer so far is Dennig Gruenling I think. http://www.youtube.com/watch?v=srXfuRWNjV8 Stuff like that.
The harshness I hear is on the beginning of the video and on some double-stops. Like on 34/5 secs. Still. The more I listen the less I hear it. But what I mean is sort of a compression or something. I would settle for that particular vht though :)
The problem is much more apparent when I play. So I'll make myself a bit vulnerable here. Made a soundcloud account.. And could only find one harp-solo in the recordings we sometimes do of our rehearsals. Still with the old mic, which has a funny chorus-thing going on in the higher registers... This was not for publication, but well.. Here goes nothing. Now that I have soundcloud, I could do something better, but I'm on a short trip now. Never mind the playing.
Last Edited by FreeWilly on Jan 16, 2014 7:32 AM
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rogonzab
458 posts
Jan 16, 2014
8:12 AM
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FreeWilly,
For what I hear you need to work on your cupping technique. Work on that for a few months and you will get rid of the harshness that you hear.
Watch how D.G grabs the mic while he is playing, and then watch how you are grabing the mic.
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Rick Davis
2880 posts
Jan 16, 2014
9:06 AM
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Freewilly, you play well. It is true that a tight seal on the harp sounds great for a lot of amped Chicago blues, but you are not playing that style. A brighter presentation is fine. You could certainly use the tight cup for effect, that would be killer. That is what I do.
I hear the harshness you are talking about, on the double stops or duo-tones on draw reeds. I hear a little beating. You could try bending the double stops very slightly to get them to blend.
Are you using the stock speaker in the VHT Specual 6? I think it is a bit shrill and does not handle the slight dissonance very well. I like the Eminence Lil Buddy speaker in the amp Nic is playing, but it's darkness may not be right for your style.
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
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Kingley
3396 posts
Jan 16, 2014
9:25 AM
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I'd agree with Rogonzab. Work on your cupping technique. What mic were you using in this clip? I find that with an SM57 or 545 I have to turn the tone up a lot on the VHT, as the bottom end is huge using a stick mic with that amp. Check out Jason Ricci's video on cupping stick mics, it may help a lot.
The mods that Mark (5F6H) mentions above make a huge difference to the VHT. I know because Mark was kind enough to give me advice on modding my VHT nd I did it to those exact specs. After those mods it had loads of bass response for an amp that size and a very nice break up . In fact the bass response was so good after doing those mods that I reversed the bass back to stock for use with an SM57 as it was too much for my taste. With a CM element in a bullet mic though it was a great sound.
Last Edited by Kingley on Jan 16, 2014 10:16 AM
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Kingley
3397 posts
Jan 16, 2014
10:46 AM
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Here's a very quick and dirty demo of my VHT with an SM57. The only mods to the VHT at this point are C11 removed, JJ 6V6 and JJ 5751. Tone is on 10 o'clock, volume is on 10 o'clock. I'm using a key of A Marine Band Deluxe.
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MP
3056 posts
Jan 16, 2014
11:05 AM
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Kingley,
That's pretty dirty tone for an SM-57. The amp has completely transformed the sound of the 57. interesting. I would have guessed it was a CM bullet or similar.
I don't know much about amps. have no idea what single ended means. I just plug in, adjust knobs, and see if I like what I hear.
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Affordable Reed Replacement
Marks Harmonica Tune-up
Click user name MP for contact info
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Kingley
3398 posts
Jan 16, 2014
11:17 AM
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Mark, Yes it is pretty dirty sounding.
The SM57 and the VHT are just a perfect match for each other.
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FreeWilly
397 posts
Jan 17, 2014
7:51 AM
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Hey Guys,
I'll post some more clips soon. With an sm57. This was my old National mic. Hopefully that will help towards a diagnose :)
I though the amp should sound good with or without tight cupping. You might want both. I want both. As Rick observes, this solo was not necessarily the place to display tight cupping. I want it to wine. Without being harsh :) That's why I play high on the harp.
I hope the speaker-swap will indeed help. I'll post some clips after that! And than hopefully get to doing the mods. Kingleys amp sounds better than mine does.
Do you use the stock speaker Kingley?
Thanks guys!
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Kingley
3403 posts
Jan 17, 2014
8:00 AM
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Yes it's the stock speaker. The JJ 5751 also makes quite a difference. I use an impedance converter with the SM57 into the high input of the amp. I presume you use an impedance converter with your mic? If not then you'll want to do that, as it will make a huge difference.
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Rick Davis
2888 posts
Jan 17, 2014
8:18 AM
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Kingley, your short track sounds good.
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
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Kingley
3404 posts
Jan 17, 2014
8:23 AM
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Thanks Rick. It was just a quick and dirty demo for FreeWilly really. I just plugged in and blew a few notes, no finesse or real structure. I should really get round to making a proper clip with it.
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Rick Davis
2889 posts
Jan 17, 2014
8:44 AM
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that is the best way, quick and dirty. sounds very good.
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-Little Rick Davis
The Memphis Mini harp amp
The Blues Harp Amps Blog
The Mile High Blues Society
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MP
3059 posts
Jan 17, 2014
10:42 AM
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Yeah Kingley! sounds good and the 57 and the VHT are a perfect match.
I've heard a similar tone from a student whom bought a 57 from me to plug into his 1963 Fender Champ.
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Affordable Reed Replacement
Marks Harmonica Tune-up
Click user name MP for contact info
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FreeWilly
402 posts
Jan 24, 2014
12:58 PM
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Tried the AT today. Sounds good.
With the sm57, my amp sounds like Kingleys with the 5751. The AT takes the harshness away. It sounds a bit duller though. I found the best set up to be the AT with some ep booster dialed in. You get the same volume and pressure as the 5751 that way, but without some of the harsher overtones. Perhaps a good nos 5751 would be the same as this set up, but those are kinda expensive around here. The 5751 gives a slightly complexer sound. Some of the complexity is harsh though. Think I'll roll like this for a while.
Sunday the speaker will probably installed. Might post an audio clip then! And will give the preamp tubes another listen.
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