Phosephene Marshall Four Hole Style Head

[HNB]

I got this cool 50 watt head in trade from fever606

"like a Marshall 1959/1987 4 hole circuit, but with only one input jack, feeding both the bright and normal channels, in parallel". Partridge transformers from a Sound City head.”

It is really cool. I got to get a look at its guts when trying to figure out why the master volume pot wasn't doing anything. Turns out it is a push pull so if it isn't pulled out, it doesn't do anything. I think it needs new power tubes. When I cranked both channels with master volume low I was getting good distortion and then I noticed popping noises and the tubes were flickering with the popping sounds. The bright channel is cool, but much noiser than the other channel. I like being able to blend the two channels or have one up or the other. Here are some pictures for the people more techy than me.

IMG_20201016_160534 by Christopher Louck, on Flickr

IMG_20201016_153451 by Christopher Louck, on Flickr

2020-10-21_12-40-01 by Christopher Louck, on Flickr

IMG_20201016_152940 by Christopher Louck, on Flickr

IMG_20201016_152951 by Christopher Louck, on Flickr

IMG_20201016_152958 by Christopher Louck, on Flickr

[fever606]

It’s a cool one for sure, glad it found a good home! Like most 4-input amps, blending the channels is where the magic really happens... this just saves you a cable!

[marqueemoon]

Those caps are not messing around.

[HNB]

They are like D batteries. LOL

[HNB]

I am going to replace the tubes when they come in. I got two matched Mullard EL34's to replace the JJ 6CA7 power tubes. I also ordered a set of three Mesa Boogie 12ax7's for the preamp. Hopefully they work. I am hoping it was just those JJ's time to go and not something wrong I did. (Cranking channel one and two together and using the master volume to have it living room volume.)

[fever606]

I’ll say those JJs had some life on them - not a particularly hard life as it was used almost exclusively for recording but they’ve put in time.

Which is another way of saying turning both channel volumes up and taming with the MV is precisely how this amp was meant to be run. The fact that I never bothered with the MV (how did I not know it was a push/pull? ) is no shade against the amp...

[HNB]

When I cranked both channels the tubes popped and flashed so I figured it was time for some new power tubes.

[HNB]

Got the Mullard power tubes today. I did my first ever bias. According to the internets, EL34's should bias around 37. When I powered it up, my multimeter showed it to be about 39. I turned the bias pot until it hit 36.9/37. Seems to be all good now. I turned the volume up on both channels and no popping or crackle. The preamp tubes should arrive tomorrow I think. Then I can seal it back up.

[HNB]

The Mesa preamp tubes came in. Sounds good to me! I wonder why the bright channel is so noisey.

https://youtu.be/1vHPIsC8zPM

[HNB]

For people who have asked in my build threads, this is the amp I have been using on my guitar demos. I have it plugged in to my Orange 4x12 with vintage 30's.

[Shadoweclipse13]

I got to get a look at its guts when trying to figure out why the master volume pot wasn't doing anything. Turns out it is a push pull so if it isn't pulled out, it doesn't do anything.

I wonder what the point of that is. Does it do something else when the push-pull is pushed in?

[fever606]

Bypasses the MV...

[HNB]

I normally use it with master volume bypassed. It is cool though if you want to crank it at a lower volume. You just pop out the push pull and you can crank one or the other or both channels.

[s_mcsleazy]

cool amp. the big issue is i really can't see the word phosphene without thinking of the imperial china album from 2010.
https://www.youtube.com/watch?v=VpVscXQeSCA

but i'm a big fan of those big ol marshall amps for clean tones.

[Dr Tony Balls]

I wonder why the bright channel is so noisey.

Could be any number of reasons. Bad solder joint, routing, failed parts or parts of an incorrect value....lot of possibilities.