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How to convert a marshall 18w from EL84 to 6L6
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Author:  CrossfireRecording [ 11 Oct 2020, 22:11 ]
Post subject:  How to convert a marshall 18w from EL84 to 6L6

Hey guys,

I'm not an expert, but I like to tinker. I have an 18w marshall(ish) clone that I've done a lot of modding to. Now I'd like to take steps to learn how to convert it to a 6L6.

What do I need to do to make that happen?

Any help pointing me in the right direction would be great. I have a local amp tech I can take it to, but this little guy is my pet, and I want to tinker haha.

I've attached schematics of what I modded, and below is a link to the latest thing I've recorded with it:
https://soundcloud.com/crossfirerecordi ... fparticles

Thanks,
Nick

Author:  gofar99 [ 12 Oct 2020, 21:30 ]
Post subject:  Re: How to convert a marshall 18w from EL84 to 6L6

Hi, I guess the question is why? However you could either make of buy adapters. I have seen some for converting the opposit way ...octal power tube sockets like 6V6 to 9 pin EL84s. So it is possible that the others exist. Check out Antique Electronic Supply (tubesandmore.com). If not you could get the bare 9 pin sockets (some might be listed as socket savers) and octals and roll your own. The actual circuit values would be close enough to try and see how it sounds. Then tweak as needed.

Good listening
Bruce

Author:  CrossfireRecording [ 13 Oct 2020, 13:14 ]
Post subject:  Re: How to convert a marshall 18w from EL84 to 6L6

I'd like to fully reconfigure the power section to be a 6L6 amp. I assume at a minimum that's a new output transformer and biasing right? I don't want to adapt 6L6 power tubes to run at EL84 power.

Author:  tubelectron [ 25 Oct 2020, 13:38 ]
Post subject:  Re: How to convert a marshall 18w from EL84 to 6L6

CrossfireRecording wrote:
I'd like to fully reconfigure the power section to be a 6L6 amp. I assume at a minimum that's a new output transformer and biasing right? I don't want to adapt 6L6 power tubes to run at EL84 power.


IMHO, @CrossfireRecording, you're loosing your time and you will devalue, not to say destroy your amp... But ti's your amp... So you do what you want, OK ?

Personally, I would never do this :eek: - and here is why :

1 - You probably expect higher power output and unfortunately, you will be disappointed : if there is an increase, it will not be significant. The power of the amp is notably (but not only) determined by the power of the supply (current and voltage). So if you want to reach at least 30 to 50WRMS - to be significant vs 18W - you will have to change the power transformer and the HV filtering, even more than the output transformer.

2 - the Marshall 18W is cathode-biased at circa 9.5-10V. A 6L6 will need circa 24-25V instead, supposing you can benefit from 350-360V of HV PSU with a idle current at 105-110mA. A Marshall 18W has a similar idle current at 100-105mA but with only 315-320V of HV PSU. Not only you need a more powerful PSU but also a higher output phase-inverter / driver to exploit the full performances of the 6L6, so it means that you may even need to modify that stage too.

3 - I do not even speak about the tone and the real power. The 18W is one of the best-sounding Marshall ever made, along with its grand brother the Bluesbreaker 2x12 combo... The 18W are obtained when the amp is fully cranked, the onset of gentle clipping (rounding of the sine waves) occuring at just 9W RMS.

Here is below a pal's 1974X RI 18W-Marshall that I had for routine maintenance, side to side with my late 70s SF PR. The stompbox on the Marshall is an EHX Holy Grail Reverv Nano :

Image

But, as I said : it's your amp, so you decide ! ;)

Cheers,

-tbln.

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