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Old 29th Dec 2018, 2:30 am   #1
Guitarist28
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Default Marshall 1930 clone

Good morning all
Its been quite a while since my last post.
I am currently planning on building a Marshall 1930 combo clone for home use. I am thinking of using modified build from Bo Hansens work (I've been in contact with him but he has now 'retired' from further work in this area) but would like to swap out the ECC82 for an ECC83 to increase the front end gain (schematic attached). Can any one offer guidance/assistance how can readily achieve this please?

Many thanks

Rob
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Old 29th Dec 2018, 7:31 am   #2
Diabolical Artificer
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Default Re: Marshall 1930 clone

Hi Rob, thought you'd legged it, nice to see you back... to get more gain on the front end you could use an 81 or 83 instead of the 82 and lose that 470k grid stopper on the 2nd half of the 82. I'd have more idea if I knew the HT at the front end, which looks to be about 250/280v without doing the calcs.

Do you know how to draw a load line? See - http://www.valvewizard.co.uk/gainstage.html on how to this, it is easy to do for a common cathode triode gain stage. This will give you expected gain, cathode R etc before experimenting or you could just breadboard it and wing it. Something like bung in a 83, reduce the first stage Rk to 1k/1k2, lose the 470k grid stopper on stage 2 and convert it to a cathode follower to "drive" the tone stack or reduce 2nd Ra to 33/47k and reduce Rk maybe.

A few thought's on the circuit - 13W is really pushing ECL86's, fine when they were 1p a dozen, not so fine now. Do you really want the tremelo? It's a bit Grandad on a tele playing twangy 50's rock n roll; lose it and the second valve and drive the LTP from a high/low gain stage. Just thought's.

Andy.
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Old 29th Dec 2018, 1:08 pm   #3
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Default Re: Marshall 1930 clone

Hi Rob, as Andy says, check out the load lines and adjust interstage attenuation to taste. First stage you probably need to maximise gain for low S/N. Cathode follower to drive tone stack is an option. I think this is something you'll need to tweek to taste when testing though. Any reason why you are going with the 1930 topology? Original design was somewhat flawed from a noise point of view, but the additional input gain stages will undoubtedly alter the feel and tone of the amp as well as reducing noise.

I'm interested to see how this goes. Please do post an update when you get this up and running.
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Old 29th Dec 2018, 3:21 pm   #4
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Default Re: Marshall 1930 clone

Thanks for your comments and yes its great to be back on the forum as I have been very busy work wise.
Perhaps you can offer some thoughts here - the reason I've been working towards building a 1930 clone is using a 'bluesbreaker' sounding amp for home use. I have tried a Marshall 18 watt 1974 handwired and its far too loud for home use. I was thinking that as the ECL86 tube has a lower output that am EL84 it might be easier to drive at less volume albeit it will still be loud. At the moment I am not sure which direction to go in as a I could build to a 1930, 1958 or 1974 design.
On a positive note I recently bought a Marshall Studio 15 of which only 500 were supposedly built. This is quite good for home use if the master volume is kept well down. This particular amp is all about tone setting rather than volume. Although it is an excellent sounding amp it doesn't have the sound I'm seeking (probably due to the 2 x 6G6 output valves.

Best Regards

Rob
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Old 29th Dec 2018, 4:22 pm   #5
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Default Re: Marshall 1930 clone

Nothing sounds as sweet as 'EL' valves for output bottle distortion in guitar amps in my opinion. Under such conditions (to generalise) American valves tend to sound flubby and fat, whereas the EL valve goes very sweet and chimey in the mid range and lose a tad of bass. The treble also distorts in a sweet, musical way. Best of luck with the project, it will be nice to see and hear (?) how it turns out. BTW, Jeff at Matamp makes truly superb repro cabinets if you're need of such a service.
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Old 29th Dec 2018, 5:31 pm   #6
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Default Re: Marshall 1930 clone

I've had a custom made cabinet built for me. I know Jeff at Matamp as I must be one of the few people that own a Matamp Little Rock. This is where 'loudness' becomes silly; its only a 4 watt amp but again it's far too loud for home use. I went for the 6V6 in this (the Marshall Studio 15 has 6V6's and not 6G6 - I don't know what I was thinking!).
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Old 29th Dec 2018, 8:03 pm   #7
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Default Re: Marshall 1930 clone

Hi Rob

I'm a bit surprised that you have chosen to use an ultra- linear output stage. i would have thought that was more appropriate to a Hi-Fi amplifier than a guitar amplifier clone.
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Old 30th Dec 2018, 2:25 am   #8
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Default Re: Marshall 1930 clone

Hi Colin
Its not my circuit design as it came from Bo Hansen. I was originally going to work to the 1930 schematic (attached). I'm not a expert by any means with regards to circuit design and upgrades but I very aware that this circuit had 2 major issues:
- it was designed at a prohibitive cost and avoided the use of a 2nd pre amp tube which I would like to incorporate as the original design was very noisy.
- the tremolo circuit was incorrect and never worked properly in the original amplifier.

I do believe that this amp was sold as a mail order beginners amplifier (e.g. Bell Musical Instruments, Surbiton, Surrey) and very few were made and sold hence the absolutely ridiculous price tag that they now sell for (2500 upwards!!).
I can remember asking my parents back in the very early 70s for a bass guitar but even at sub 100 it was far too expensive.

Best Regards
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Old 30th Dec 2018, 7:56 am   #9
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Default Re: Marshall 1930 clone

What are you after exactly? First not a loud amp but at the same time you want that distortion valve amps give when overdriven and that all elusive "sound".

If you read Valve Wizard's site he goes into great detail about the different tones and sounds you can get by biasing a valve a certain way, changing the cathode resistor etc. The OPT has a lot of influence too (not forgetting the guitar, it's PU's, it's tone control's, strings, body etc, etc).

One approach is to find an amp that has "it", use the front end of this to drive a low OP stage. You could use a QQV03-10 (2x 5w beam pentodes in one bottle) as the OP stage or go Class A SE, but this present's it's own problem's. Whichever, I think you'll find it easier to build your own than random amp building or buying, that way you'll find "it", but the road may be long and hard : )

There is of coarse another way, that's to use amp/cab software, I've heard this has come on leaps and bounds in recent years though haven't tried it recently

One other good source of info is the AX84 Project, those lads over there know a lot about guitar amp building - http://ax84.rru.com/projects.html. This - http://www.guitarstudio.tv/documents...Amplifiers.pdf is well worth a read too, it is one the best sources of info re guitar amp building.

Andy.
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