Starting added tube 50w using Marstran chassis & iron

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

Postby neikeel » Sat Jun 08, 2013 9:04 am

I use Mullard ECC83s or Brimars as long as they are BVA or from Holland and test normally I am not picky.

Never seen a Genelex Gold Lion ECC83 :|
Neil
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Postby ivan H » Sun Jun 09, 2013 3:06 am

IIRC, someone on the Metro Amp forum also reccomended a Mullard in the 1st position of these. I havent actually seen a Genalex Gold Lion ECC83 either. 1 of the valve suppliers here (Evatco) list them on their site as a 12AX7/ECC83/B749 (gold pins) at $49 a throw, almost double the cost of most other 12AX7's. I emailed them to enquire about but havent heard back yet. Since reading the last page of the SIR 100 SL thread on the Metro forum I added the 10k dropper & 22uf filter on the added stage (off the node at the CF as Tim Caswell reccomends) so that I can properly condition it while waiting on the valves to arrive. I wired the board on top so its easily changed so I'll try with & without it. I'll get some valves into it & biased up later this week & get to tweaking. I'll also get those switching system & other pics up 4 u. Cheers
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Postby ivan H » Sun Jun 09, 2013 11:45 pm

Ok, I found some info on the Genalex Gold Lion ECC83 (listed also as a B759 there) in a comparison of 12AX7 types on thetubestore's site. It is a Russian tube & apparently 1 of the better new types. A large plate design that has very good noise & microphonic characteristics. Featuring a broad midrange responce that is pleasing to the ear, voiced with a full midrange & nicely controlled highs & lows. Couldnt be made to feedback (microphonic) at major sound pressure levels in a combo type amp. Reccomended for the JCM800 series to tame the brite channel & cut some of the "crazy high end." in the 1st gain stage of a guitar amp it will sound warm with real creamy drive when pushed with hotter pickups,,,, or so the review says. So,,,, maybe I'll give 1 a try, these type amps being prone to squeal etc, it may suit, tho at $49 I'll pay the extra few bucks to have it thoroughly tested for microphonics & noise. Luckily, I have a pretty good relationship with that particular supplier here. I got some close up pics of the relay PSU & switch/indicator to my friend today Neil, so they should be up soon. Edit; Tubedepot also list some of the Genalex Gold Lion series including the KT88, KT77, KT66, B749 (ECC82) & B759 (ECC83), & saying to keep an eye out for more of these great new production tubes from russia so I take it they are some of the better new tubes available. Cheers
Last edited by ivan H on Tue Jun 11, 2013 6:51 pm, edited 1 time in total.
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Postby ivan H » Mon Jun 10, 2013 8:16 am

Image

pic 1; PPIMV with 2.2meg carbon films. Shield on leads from PI connected to position 3. Brown wire carries bias voltage to pins 1 of dual pot. Shields on leads to pwer tubes connected to bias supply at pins 1. Shield on leads from PI carries well past tip end of speaker jack socket as it is positioned quite close to.



Image

Pic 2; 10k HT decoupler & 22uf/450V electrolytic. Blue 100pf across 2nd stage plate resistor & yellow 220pf across added stage.



Image

Pic 3; Shows the panel mounted relay switch & below it is the LED. Also below the switch can just be seen the small blue & red wires exiting the heatshrink. The red carries the +5VDC from the PSU & connects to the relay's coil. The blue wire carries the + voltage from the PSU to the LED's anode. The 2 orange wires from the center terminals of the switch go to both the relay coil & LED cathode (activating grounds). The lower terminals on the switch connect to the ground bus at the footswitch jack socket. The center & lower terminals on the switch also have a .1uf/100V greencap across them. The red wire on the top terminal of the switch goes to the tip connection of the footswitch jack socket.



Image

Pic 4; Shows the 7805 regulator, the 4700uf/35V filter & 1k voltage dropper for the LED. The regulator's lower red lead is from the voltage doubling rectifier. The black center lead is its ground & the top orange lead is its +5V output. The red lead also connected to this tag with the orange lead & caps + is the + voltage to the relay coil, the blue on the end of the 1k goes to the LED's anode. (the 1k resistor could also be mounted directly between the relay's coil & the LED if u wanted).



Image

Pic 5; Shows the whole relay PSU. The tags at either end of the strip are ground. The 4 tags on the right have the two 4700uf's wired in series on them. The cap -'s are to the right. Note that the middle 2 terminals are bridged. 1 side of the 5VAC PT winding connects here . The 5th tag from the right has 2 diodes of opposite polarity connected to it. The other side of the PT's 5VAC winding also connects to this tag. 1 diodes cathode goes to the + while the other diodes anode goes to the - at either end of the 2 caps in series, to form the voltage doubling rectifier.

[Hi ivan, I hope you don't mind. I've added the captions underneath your pics for you. -Dai] (no, I dont mind at all, thank you very much. Cheers, Ivan)
Last edited by ivan H on Wed Jun 12, 2013 9:48 pm, edited 2 times in total.
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Postby ivan H » Mon Jun 10, 2013 9:16 pm

I cant seem to put text in the right place using my phone this morning, maybe more coffee. Anyway, pic 1; PPIMV with 2.2meg carbon films. Shield on leads from PI connected to position 3. Brown wire carries bias voltage to pins 1 of dual pot. Shields on leads to pwer tubes connected to bias supply at pins 1. Shield on leads from PI carries well past tip end of speaker jack socket as it is positioned quite close to. Pic 2; 10k HT decoupler & 22uf/450V electrolytic. Blue 100pf across 2nd stage plate resistor & yellow 220pf across added stage. Pic 3; Shows the panel mounted relay switch & below it is the LED. Also below the switch can just be seen the small blue & red wires exiting the heatshrink. The red carries the +5VDC from the PSU & connects to the relay's coil. The blue wire carries the + voltage from the PSU to the LED's anode. The 2 orange wires from the center terminals of the switch go to both the relay coil & LED cathode (activating grounds). The lower terminals on the switch connect to the ground bus at the footswitch jack socket. The center & lower terminals on the switch also have a .1uf/100V greencap across them. The red wire on the top terminal of the switch goes to the tip connection of the footswitch jack socket. Pic 4; Shows the 7805 regulator, the 4700uf/35V filter & 1k voltage dropper for the LED. The regulator's lower red lead is from the voltage doubling rectifier. The black center lead is its ground & the top orange lead is its +5V output. The red lead also connected to this tag with the orange lead & caps + is the + voltage to the relay coil, the blue on the end of the 1k goes to the LED's anode. Pic 5; Shows the whole relay PSU. The tags at either end of the strip are ground. The 4 tags on the right have the two 4700uf's wired in series on them. The cap -'s are to the right. Note that the middle 2 terminals are bridged. 1 side of the 5VAC PT winding connects here . The 5th tag from the right has 2 diodes of opposite polarity connected to it. The other side of the PT's 5VAC winding also connects to this tag. 1 diodes cathode goes to the + while the other diodes anode goes to the - at either end of the 2 caps in series, to form the voltage doubling rectifier. Hope this helps Neil, & I hope u understood my explanation. Cheers
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Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Fri Jun 14, 2013 12:13 am

Ok, so I ordered 1 of the Genalex Gold Lion ECC83/B759's & also a re-issue Mullard ECC83's to try. Physically, these 2 types look like the plates at least could be made with the same tooling, with the Gold Lion having a darker color coating on the plates than the Mullard. Plate length on both types is 15mm. The Gold Lion also has well gold plated pins. I have read that the re-issue Mullard has tone that is similar to but lacking the 3D quality of the origonal long plate Mullard, so I dont have great expectations for it, but without trying 1 I'll never know. I might try it in my other 50 watter. I'm just waiting on the winged C's & Tung Sol ECC803S to arrive from another supplier (they take twice as long as the supplier these came from) so I can get to tweaking this amp. There is an annual antique radio society swap meet here locally in September that I am hanging ut for to hunt for some NOS tubes & components. I missed the last one due to being away, I wont be missing this one. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Mon Jun 17, 2013 1:41 am

Ok, again the BC 22uf/450V electrolytic took less than 1/2 hour to properly condition, thank you Robert at Valvestorm. The rest of the valves have arrived so this evening I'll bias the EL34's up & check all voltages etc. Any play testing b4 the weekend will have to be done with the PPIMV well down as cranking it even some would not impress the neighbours (well it hasnt when I've done it in the past), but at least this will give me a chance to sort the variable NFB out. I have a 50k & 25k Lin pots for this (none installed yet). I'm not looking to increase the resistor value above the 47k, rather just to be able to lower the value to keep the presence & resonance controls active when the PPIMV is turned down. Hopefully with the 22k resistor/25k pot/8 ohm tap it'll be good & allow me to install a .68uf bypass across the 820 ohm cathode b4 the cathode follower, as I usually like the V2a 820/.68uf & 47k/8 ohm combination. I have an A cab loaded with two re-issue greenbacks (English, not Chinese) & 2 Vintage 30's, with two series wired pairs paralleled at the jack (16 ohms) for this amp. Anyway, I'll get to it this evening & post again in a day or two. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby neikeel » Tue Jun 18, 2013 6:21 pm

Good to see progress, also interested to hear how the variable NFB works. I am looking to cover the options from 16ohm/27k through to 4ohm/100k so the 27k resistor sounds like a start, just need to calculate optimum tap and pot size to get the correct equivalents.
Neil
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Thu Jun 20, 2013 10:00 am

Hi, I meant to post this a few days ago, but have been away for few days & forgot to take the voltage chart I noted after biasing the EL34's to just under 70% MPD, being 38mA/441V. The voltages throughout are; V6 & V5, plates 441V, screens 436V (I havent checked screen current yet), control grids -47V. All pre amp tubes are rotated 180 degrees putting the a triodes towards the power tubes, so I will list the a side the the b side on all. V4 (PI) plates, a 210V, b 209V, cathodes 37V. V3a plate 297V, cathode 160V. V3b plate 160V, cathode 1.011V. V2b (added) plate 253V, cathode 2V. V1a plate 245V, cathode 2.554V, V1b plate 203V, cathode 1.809V. As it was early night time when I baised etc & there are infant children at home, I could only give it a quick, low volume play test, with the 2 gains & pre PI master also well down to not possibly produce squeal at the kids bedtime, but I did check the presence & resonance controls effectiveness at this level (Ive not used a master b4) & I think that Neil may be on the right track thinking of using the 16 ohm tap in conjuction with a variable NFB. I'll spend a lot more time on the amp this weekend & get back 2. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Tue Jun 25, 2013 6:57 pm

Ok, I've put several hours on this amp now & am pretty happy with it. I've read that these type amps can be really noisey & prone to squeal. Thankfully I have no noise or hum issues, even to I havent made a head cab for or have an under chassis shield yet. I bolted it to a piece of ply with the grey rubber feet attached to & sat it on the concrete floor to minimise picking up interferance which seemed to work well enough. Squeal wise, well it can be made squeal but I dont think its bad. With gain 1 dimed, bringing gain 2 over half results in squeal but backing off gain 1 a little to around 9 or 8 1/2 solved the problem & gain 2 can be turned right up without squeal, tho on 10 its on the edge of stability. So last evening I changed out the 2nd stage plate bypass from 100pf to 220pf. Hopefully this will be enough to get rid of mst of the problem. While at it I checked the screen current which is 5.3 & 5.6mA, so I biased a little hotter at 40mA actual plate current at 435V. My main interest in building this was the #39+, & it doesnt disapoint. This is a 2203/4 on steroids, but with 2 gain controls plus a pre & post master the pre amp distortion can be much better shaped and being able to overdrive the PI at lower volumes thickens &adds more body to the tone. Switching channels is pop free, at least at the moderate volumes I was playing at & there is no noticeable difference in volume. The 36 mode is more clipped & the 10k/.1uf cathode moves the roll off point up a fair bit so a lot of lows are taken out. I'll see this arvo if the 220pf over the 2nd plate helps with squeal & explore it some more. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sun Jun 30, 2013 9:41 pm

Ok, so I've put a fair bit more time on this thing during the weekend & really dont feel the need to change too much. Uping the 2nd stage plate bypass to 220pf seemed to help with the squeal issue so I'll leave them as they are for now. I've learned to live with the NFB as is, the presence & resonance become active with the post master opened up a little so I'm ok with that for now. The hot shield I made works well to give that cocked wah effect. The only thing that I'm thinking of is maybe to try removing the .22uf on the 2nd cathode just to try it as a #39 rather than #39+, in order to get more seperation between channels,,,, & maybe try it without the 150k across the gain 1 pot to see if I can do without it. Other than that I'm happy with it. I dont feel the need to tweak madly chasing Slash's exact AFD tone or anything like that, just to be able to switch to a good lead tone which it has. I've been playing a Gibson custom shop Zakk Wilde (passive) thru it, which I've been wanting to change the pickups on, however thru this its not so bad,,, seems to suit kinda thing. Yesterday I plugged my ES335 thru it with both gains down a little & wow,,, it sounds,,, freakin great. Mind you, that was at low volume, it'll be good to try at decent volume. I really need to plug a few different guitars thru it to fully explore it. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby neikeel » Sun Jul 07, 2013 9:05 am

How have you found the NFB control?

As you are you have 47k on 8 ohm tap with NFB pot on full and have facility to decrease the pot value to allow more NFB back into the amp as you increase the PPIMV?

Is the foot-switch working ok for you? I thought about using my AFD type amp at thw gig last night but took my AC30 and the JTM50 pairing instead :D .
Neil
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sun Jul 07, 2013 5:46 pm

Hi Neil, I havent fitted variable NFB yet, a 100k Linear pot & few other components should arrive tomorrow so I'll let u know. I have a 25 & 50k but thought I'd use 100k. With a 27k resistor I'm thinking a 100k pot with a 270k resistor across the pot (to bring the pot to around 73k) I'll have 100k NFB with it right up, down to 27k which I'm hoping will do. I'm aware that putting the resistor across the linear pot will result in a rather pronounced logarithmic taper but this should suit, giving finer adjustment down the low end of the pot & progressively getting coarser as its turned up. The switching system works well, no poping or any other problems. Everything else is still the same, tho I may try removing the .22 on the second cathode so its more 39 than 39+ (or maybe swap its position with the .1uf & remove the .1uf to have 39/39+). Other than that it doesnt need much tweaking at all I dont think, just change the polyester caps to Sozo's when their back in stock. I also have an Electro Harmonics 5751 (gold pin) on the way to try in the added position as I've read a few people like this lower gain type tube there. A little down the track I'll order some NOS pre amp tubes from Tube Depot, once I've settled on wot to use where. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sat Jul 13, 2013 2:32 am

Ok, I guess its time to do a few tweaks, I've just been enjoying playing this thing, but roylfuchs posted a few circuit details of his recently Tim Caswell modded Metro amp so that has kinda inspired me. A few details,,, it sounds like he has a 39+ mod, at least. The 1st stage's cathode resistor is 1k with an unknown value bypass cap. So by my (maybe wrong) calculations, to get roughly the same rolloff point as a 2k7/.68 cathode (86.69hz), a 1k would need 1.83uf to give a rolloff point of 86.97hz. I've this morning got a couple of 35V tantalums, a 1.5uf & a .33uf that I'll parallel across a 1k & give it a whirl. He also says the coupling cap on the input side of the added stage is an 0.0022, which I have a Sozo of spare as I ordered 2 of for this build but so far have only used 1 of in the peaker after the 1st stage. He also has the added stages cathode bypassed with a 0.22uf, which I have on the 1st 10k cathode (which he doesnt mention), so I might try it in that position. I have resisted bypassing the added stages cathode so as not to jam too much signal into the cathode follower so it may need to be limited somewhat with this arrangement, I guess we'll see. I'll also do the variable NFB thing,,, I might try it just by changing the resistor on the board at first to see how it affects it, rather than put a hole in the back panel straight off. I'll do all tweaks 1 at a time & check results, I'll post how things go. Just a few random thoughts,,, I know that Caswell's later development of the mod, the #39GL (George Lynch) uses 2 unbypassed 10k cathodes in 39 mode, adding a 0.1uf over the 1st 10k cathode in 39+ mode & adds a 0.22uf over the 2nd 10k cathode in 39++ mode. A 10k cathode bypassed with a 0.1uf gives a rolloff point of 159.15hz. If he's using a 1k cathode resistor on the 1st stage, bypassing that with a 1uf cap would also give a frequency rolloff point of 159.15hz,,, now it would make sense to use that value, & knowing how bright the amp reportedly is, I'll definitely also try this. I'll have to get to a friends to try & get some clips recorded & posted,,, now thats going to be a mission. Cheers
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Re: Starting added tube 50w using Marstran chassis & iron

Postby ivan H » Sat Jul 20, 2013 4:02 am

Ok, so I have replaced the 47k NFB restor with a 27k & with the PPIMV on about 1 or 1 1/2 the presence & resonance are becoming active, tho the effect is limited. I do like its affect on the power amp tone at this low level. It seems clearer, more defined or articulate with less fizziness, so I'll add a 100k linear pot & go from there, maybe reduce the value of the resistor even more. Does anybody have any idea how low the value of this resistor can safely be taken? I have read someone on the Metro Amp forum saying they had experimented with as low as 10k, so I may go a little lowet to say, 22 or 20k. I have also added a 0.6mm thick alloy shield under the chassis, with 3/4'' DIA holes for the captive nuts to pass thru so the chassis bolts down properly. This has helped a bit, even tho it wasnt bad b4. It has also helped with squeal with both gains & pre master cranked, so I'll add the NFB pot then do a little with the pre amp. Now that I've been putting some time on it, its starting to loose some of that new amp feel & sound even better. I didnt think the standard Sozo caps needed a wear in period, but either way it is seeming to sound livelier & better with more time on it. I'vr also been going over the self help links thoughtfully posted on the Amp Spa forum by member dal h (thank u very much) & mighy try a different approach to the plate bypass caps as suggested in the ''caps to ground of pre amp plates'' link. Maybe try a 100~220k series resistor on the plate side of each bypass cap, see how it goes, altho with the squeal reduced by adding the shield (it was only squealling with gains & master maxed) I'm hoping I can reduce the size of or do away with the plate bypasses.Cheers
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