Starting added tube 50w using Marstran chassis & iron

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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sun Jul 21, 2013 6:14 am

So I added a 100k Linear pot for the variable NFB control & have tested it a little. I'm thinking I'll change the presence cap to a 0.1uf for mment as it will make testing a bit easier as its effect is more pronounced, tho with the 0.68uf in there I could notice that it does work, even tho I couldnt open the PPIMV up all thatuch today as we had visitors over,,, about 4, where the presence &resonance wete startimg to become reasonably effective with the NFB control down low. Turnung it up took them out. I'll change the presence cap & play with it more tomorrow arvo. I'll probably also try removing the 150k across the gain 1 pot. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby neikeel » Sun Jul 21, 2013 6:07 pm

ivan H wrote: I'll probably also try removing the 150k across the gain 1 pot. Cheers


Good luck with that :wink: (have your earplugs handy for the squeal!)
Neil
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sun Jul 21, 2013 10:20 pm

U've obviously tried this,,,, maybe a 250k pot. I've read others saying they prefer the tone without the resistor, tho most dont mention thr pot's value or squeal. At the moment this is ok with regard to squeal. I have a 5751 as the added stage & can turn both gain controls right up, & the pre master without squeal, whereas with the ri Mullard in there it would sometimes squeal when the master was up high. I like the crunch the 5751 gives without harshness. Well, I'll play around a little & see how things go. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby Did J » Wed Jul 31, 2013 1:55 pm

Awesome report about your amp building, it was great to read you week after week and I learnt a lot, thanks to share your experience ivan.

... and Neikeel too indeed 8)
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Wed Jul 31, 2013 9:51 pm

Hi, glad u've found it interesting. Neil's input has been a great help. He's very knowledgeable in this field. His input is much appreciated. Since my last visit I have changed the NFB resistor to an 18k & the pot to a 50k with a 68k resistor tacked across it, so its variable from 18k ~ 46k8, (approximately). I generally like the V2a 820 ohm/.68uf combined with a NFB 47k/8 ohm tap so will try adding the .68uf bypass. Hopefully it wont slam the crap out of the CF. Its also about time to start tweaking the pre amp for more of a difference between the 2 channels. Maybe 2 unbypassed 10k cathodes for 1 channel. Cheers
ivan H
 
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sat Aug 10, 2013 11:54 pm

Hi, its been a while, everything been all good with this amp & I love playing it but I have wanted more variation between the 2 channels so yesterday I got into the pre amp, first taking it back to a stock #39, being the normal MV circuit with 470k/500pf peaker. I didnt use the bright cap on the pot. Out from the second stage thru another peaker, I then deviated from the normal #39 circuit with the use of a 1 meg pot with a 470k across it, as suggested to me by Rockgod212 & into the addded stage with unbypassed cathode resistor & very large value of 2200pf plate load bypass. From there its as b4. I havent yet added the .68 bypass to the 4th stage's 820 cathode resistor. I like this circuit as 1 channel as its like a bright 2204 but with "more." Areas I'll be looking at are the peakers & the plate load bypass on the added stage, plus maybe the pot's value before the added stage, maybe a 250k with a 68k resistor between the pot & ground. Maybe put the signal straight to the wiper again as I dont mind this trick. The 2nd channel is the #39GL (George Lynch) channel. This switches in the 2 cathode bypass caps, a .1uf on the 2nd & a .22uf on the added stage. This really boosts the gain a fair bit, & clips the signal a lot. More than it clipped the way I had it b4. It also cuts more of the low end, which is a good thing with it clipping this much to avoid muddyness. I did have both gain 1 & 2 on 10 & the pre MV on 8 as I was looking for squeal, which with that large plate load bypass there is none of, so I'll look at reducing this as much as possible. Switching in the 2 cathode bypasses of course brings with it an increase in hiss/noise, which in the #39 mode is really very good, even when cranked with a stratocaster thru it. The #39 channel is very Marshall, even tho its bright. I can very much hear the guitar type plugged thru it. Cranked it also gives plenty of distortion, kinda like a Nigel Tuffnel deal (goes to 11) plus some. So I think I'll keep it like this, as the 2 channels are now distinctly different but both are good useable tones that will cut thru really well. So maybe I'll try larger value caps for 1 or 2 peakers for more mid growl, maybe try a 47k slope resistor. The .68uf fot the 4th stage's 820 cathode resistor,,, I could put it on the other side of the 1/2 of the relay that is switching the .22uf on the 3rd cathode, as both share the same ground point. This would mean the .68 would be switched in for #39 mode, bit switched out for #39GL mode as I really think it would be too much. The bypass caps on both 2nd & 3rd cathodes really does give a lot of gain & produces a LOT of distortion. So, I'll get back when I've done a few more tweaks. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sun Aug 11, 2013 7:55 pm

Ok, after playing this a little I'm going to at least either only partialy bypass the added stage or remove the bypass cap altogether. Its just too extreme for my needs. I remember reading wot Caswell said about having to put a second gain control in the Lynch heads in order to manage the extreme level of gain as the bypasses werent switchable & always on. I've found I have to dail them back in this mode & then when I switch back to the stock #39 channel its turned down too much. So I'll experiment a little, its easy enough to swap the bypasses around a little on the 2nd & 3rd stages. I guess this is wot tweaking is all about,, finding wot works best for your own particular needs. I will try the .1uf on the 2nd cathode 1st. This is putting it kinda like the 36 spec people are using & with not having the 150k across the gain 1 pot I dont think I'll need to drop the 3rd cathode to 5k in this mode. This will free up 1/2 of the relay so maybe I can use this to switch the value of the cap in the 1st peaker, unless it causes interference problems. Hopefully it wont & when switching in the .1uf cathode bypass I can also switch a .0022uf peaker cap in. This would give a spec close to wot people call #36. For the other peaker cap I'm thinking a .001uf to try to get more upper mids. I do prefer the tone without the 150k across the gain pot. It requires reducing the drive to the added stage (the 470k across gain 2 pot) but I like it much more this way. Cheers
ivan H
 
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Thu Sep 19, 2013 12:35 am

Hi, its been ages since I've been here, I've been playing the sh*t outta this thing. I love the #39 Marshall on steriods thing & really never much switch it to the #36ish channel. Have made a few changes but nothing major. NFB loop consits of being taken off the 8 ohm tap, 0.0047uf/1Meg Lin resonance control, a 50k Lin pot with a 68k across it for Variable control, a 1k & an 18k in series on the board & a 5k Lin pot/0.1uf presence. With the variable control on zero the 19k/8 ohm tap is roughly equivalent to 27k/16 ohm tap. With the pot at maximum its about 47k5 off the 8 ohm so I also added the 0.68uf bypass cap across the 820 ohm cathode b4 the cathode follower. I've always liked this with 47k/8 ohm NFB & I like it in this too.
The pre amp is pretty much the standard #39 now, with 1 or 2 minor differences. Input thru 33k (which I'll change to 68k), 2k7/.68uf cathode. 100k ra, 0.022uf coupler to a 470k/560pf peaker. 1 meg pot with no brite cap. No grid stopper, 10k rc, 100k ra, 0.022uf coupler, 470k/500pf peaker, 1 Meg pot with 470k across it, no brite cap, no grid stopper, 10k rc, 100k ra with 0.0022uf bypass, 0.022uf coupler, 470k/500pf/470k peaker/rg, 820 ohm/0.68uf rc. Tone stack is 560pf/33k. The footswitch only switches in a 0.1uf across the first 10k rc, also adding a bit of hissy type noise, of course.
So, from here I'll try a 68k instead of 33k grid stopper in the input, just to see which I prefer. I'll also try putting like, 220k series resistance b4 the 0.0022uf plate bypass on the added stage (from dai h's self help links, amp spa), & also experiment with smaller value caps for this bypass. Other than that, I'm completely happy with. No need for my TS9 tube screamer now. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby neikeel » Thu Sep 19, 2013 5:55 am

ivan H wrote:Hi, its been ages since I've been here, I've been playing the sh*t outta this thing. I love the #39 Marshall on steriods thing & really never much switch it to the #36ish channel. Have made a few changes but nothing major. NFB loop consits of being taken off the 8 ohm tap, 0.0047uf/1Meg Lin resonance control, a 50k Lin pot with a 68k across it for Variable control, a 1k & an 18k in series on the board & a 5k Lin pot/0.1uf presence. With the variable control on zero the 19k/8 ohm tap is roughly equivalent to 27k/16 ohm tap. With the pot at maximum its about 47k5 off the 8 ohm so I also added the 0.68uf bypass cap across the 820 ohm cathode b4 the cathode follower. I've always liked this with 47k/8 ohm NFB & I like it in this too.
The pre amp is pretty much the standard #39 now, with 1 or 2 minor differences. Input thru 33k (which I'll change to 68k), 2k7/.68uf cathode. 100k ra, 0.022uf coupler to a 470k/560pf peaker. 1 meg pot with no brite cap. No grid stopper, 10k rc, 100k ra, 0.022uf coupler, 470k/500pf peaker, 1 Meg pot with 470k across it, no brite cap, no grid stopper, 10k rc, 100k ra with 0.0022uf bypass, 0.022uf coupler, 470k/500pf/470k peaker/rg, 820 ohm/0.68uf rc. Tone stack is 560pf/33k. The footswitch only switches in a 0.1uf across the first 10k rc, also adding a bit of hissy type noise, of course.
So, from here I'll try a 68k instead of 33k grid stopper in the input, just to see which I prefer. I'll also try putting like, 220k series resistance b4 the 0.0022uf plate bypass on the added stage (from dai h's self help links, amp spa), & also experiment with smaller value caps for this bypass. Other than that, I'm completely happy with. No need for my TS9 tube screamer now. Cheers


Great! I will try the NFB thing when I get time. I will stick with my preamp for now 8)
Neil
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Thu Sep 19, 2013 6:52 pm

Hi Neil, I wanted to keep close to the 47k value with the pot maxed as I find the the V3a 820/.68uf cathode gets a bit much with less negative feedback than that. I found a post from flemingrass on the Metro forum explaining the relationship betweem the OT's 3 secondry taps from which I calculated that a 19k/8 ohm combination gave the same amount of feedback as 27k/16 ohm, which is also stock Marshall & gives the most feedback they've used (possibly #39 could have had this combination as I have 1959T schematics showing this). So its not a vast amount of variarion but it varies between 2 standard values & as 27k/16 ohm is quite a bit of feedback it works well enough at keeping the resonance & presence active when rolling the PPIMV back. The 50k pot with 68k across gives 28.81k so it tops out at 47.81k, not the 47.5 I said earlier, but its close enough to 47k. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby BennyRodgers » Sat Sep 21, 2013 8:12 am

ivan H wrote:Hi every1, I've been wanting to do an added tube (Caswell #39) type build for a while & have finally got started. I had hoped to use the 50watt trem/mod chassis that Brian was trying to get happening, but when this didnt come to fruition Brian kindly offered to drill 1 o his existing chassis for an extra pre amp tube, thank you very much Brian. Very nice chassis too. The PT is Brians 1202-118 & the OT I chose is Brians custom 50 watt Dagnall clone. Choke is Brians 3h C1999. I am waiting on the last order from Robert at Valvestorm to arrive which contains the front & rear panels, ARS eletrolytics, pots & a few other components so I'll have to wait until then to get right into it. As I dont need it to be period correct or anything I'm using a Metro Amp plexi front panel & one of Sparky's rear panels. So far I have the transformers & choke mounted along with ceramic valve sockets. All pre amp sokets have been rotated 180 degrees so the input goes to V1b first, as this is supposed to be the "quieter" side of the tube, & all components are then all laid out in the correct order on the board without the signal crossing over earlier stages anywhere. V2 is only 1/2 heatered with V2b's heater being connected only. Brian added the socket hole between V2 & V3 which fits in perfectly with the board layout with only the two 10k pre amp HT voltage droppers/decouplers being arranged differently to make it all fit neatly. These two 10k resistors I have arranged "in line" rather than side by side. I also "squeezed" the tone stack slope resistor down by 1 turret space (or hole space) on the board. These 2 changes freed up 2 rows of holes on the board so now components for the last gain stage/cathode follower, which has been moved are in the correct place relative to the tube. For heater wiring to the power tubes I have used solid 18g green cloth covered heater hookup wire, then the standard 22g red & black led light for all pre's. The heater CT is connected to position 1 of Larry's grounding scheme with the solid 18g wire. For the turret board I got a blank piece of Brian Haberman's nice board material & have populated it with turrets myself. It is not that different from a stock 50 watt board. I have Sozo coupling caps & most of the resistor will be a mix of 1/2w & 1w Vishay Dale metal films (for a low noise floor), with a few carbon films. Voltage droppers/decouplers are 3w metal oxides. I have made up the input hot shield by using the normal green 22g wire (from Valvestorm's plexi wiring kit) which I inserted into a 4" piece of braided sleeve & then covered with double walled heatshrink. The board is wired & partially populated with components. I have pics so far & will keep a good record of the build with pics that I will have to take to a friend with a computer to upload (as I'm computer illiterate). I would very much appreciate any tips from any 1 who has completed this type of build before. Cheers

hello friend were you able to complete the build? It seems very exciting and I would love to implement it.. Can you give some useful tips?
Last edited by BennyRodgers on Sun Sep 22, 2013 8:46 am, edited 1 time in total.
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sat Sep 21, 2013 10:10 pm

Hi friend, completed,,, well its still not in a head cab yet. I have it mounted on a piece of ply wood with a 0.6mm thick alloy sheet between the amp & ply to shield it, with the rubber feet screwed on & the whole shebang sitting atop the 4x12 A cab. I got the cab empty & loaded it with 2 Greenback RI's (English) & 2 Vintage 30's (Chinese), wired with a GB & V30 in series in each pair, with both pairs paralleled at the jack (16 ohm). The speakers are arranged in an X Pattern.
I've had it up running for, well, quite a while, check post dates would tell u. I've changed things around a bit to find exactly wot I like, but basicly just variations on the 2k7/.68uf first stage cathode followed by a 10k cathode on the 2nd & 3rd stages theme. With this basic format u cant really go wrong, just tweak to suit ur own personal needs.
Any tips or recommendations, well first up I'm glad I got Brian to drill the chassis for the extra tube rather than have a go at doing myself as I dont have a drill press so its much neater than if I hada done it. Rotating the pre amp tube sockets 180 degrees & having all components in the correct order of placement in regard to the signal chain, without the signal crossing back over itself anywhere was a really good idea. (I think I phrased that correctly, to make sense). Half heating the added tube I think is a good idea. I know a lot of people just hook both heaters up, but I didnt in the interest of noise or other possibly issues.
Other than that, I would say pre think wot u want from the amp. Do u want it as just a straight out lead type amp that u will use in conjunction with another amp or two, or do u want it as a multi channel type amp that u can switch between 2 or 3 distinctly different tones with. I use mine as basicly just a lead or overdriven tone amp & use an A/B footswich to switch between it & another 50 watt build with its own 4x12 cab. If u want a multi channel format, Neil's setup is extremely versatile, going from a 1959 type pre to a 2203 pre to a #39+, all in one amp & using just a push/pull DPDT switch type pot & an A/B switch, that is very well thought out. He is also very helpfull. Genuine good guy.
Other than that, if u think u'd like an amp like this, have at it. As soon as u plug into it & rip out a few licks, u'll know exactly why Lynch, Slash & every one else who try it instantly love it. The term "Marshall On Steriods" is an apt description. Cheers.
One more piece of advise, go to the Metro Amp forum & check out
the Caswell #39 amp related threads, there a few of em, or the AFD & Levi #36 related threads & also the epic 550 page thread entitled "SIR 100 Watt Superlead" for all the info u would ever need on these sort of amps. Cheers
ivan H
 
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