6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

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StarGeezers
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Post by StarGeezers »

Extensive testing With the Band , has indicated the last changes were Not too bright at all , and now I have not only the Pentode sweet Tone , but the “cut” I needed to be heard over the 6 other players.... a little bright for “bedroom” playing , Perfect for gig use ... Been a couple weeks now since the last mods , others have played on it too and Like it ... so it will stay this way for a while ... Happy at last .... for now ... :roll:
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Dustpuppy
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Post by Dustpuppy »

SG, I'm glad you found a sound you like!
I've been having a lot of fun playing through a hybrid of the abmin with half a 12ax7 in front of a 5654 pentode and 6aq5 power tubes.
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StarGeezers
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Post by StarGeezers »

DP , after months of testing/playing , we’re still Very Happy with the amp ... :D :D :D
Something NICE about the 6SJ7 /5693...
Can you tell us More about your amp .... Please ....
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zaphod_phil
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Post by zaphod_phil »

Does it have much resemblance to a Marshall 18W?
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Nature abhors a clean tube amp

StarGeezers
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Post by StarGeezers »

Having never owned a Marshall 18 watt , I can only say .... Maybe ???? The extensive changes have made it much Brighter/ tighter than the original amp presented ...
We’ve had other Higher powered Marshalls , and they sounded Good , but don’t /didn’t have the “sweetness” of Tone (Cleans ) that this one has ... JMHO
We recently had a Marshall 30watt amp (EL84s) in for repair ( overheating and rectifier block dropped out :o ) and once fixed , it sounded really nice , especially overdriven ... can’t say as we compared it though .... just glad to get it done and out of the shop , cause’ it was a PIA to work on and it bit me twice, despite the usual cautions ... grrrrr!!! 8O

I did compare it to my new 5E3 “Special , which is very Fender’y (naturally) , and it’s sorta similar in tone , but again , the Cleans are sweeter with the 6SJ7 ... Just something Nice about that tube ... Playing distorted (more so lately) both amps sound really Good ...

Just as a point of interest , last week we had avery OLD Princeton (Brownie ) come in for repairs , and that one had a really SWEET clean sound ( and Great OD tone too) ... for some reason which I’ve yet to figure out ...

ZP, we really appreciate all the help getting this sorted ... THANKS !!! :D

Hoping to get more info soon on DPs amp with the tube in front of the pentode ... Thinking that should be really Nice , with the added gain ... 8)
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Post by brewdude »

SG, I have been working on an amp (not an 18 watt) with a paralleled 12AX7 (LED biased) into a 5693 (set up a little different than the ab.min./01 pentode) into a paralleled 12AU7 Cathodyne PI feeding a pair of 6V6's. It also has a more complicated power supply with a choke right after the reservoir cap and a VVR controlling the PI and PA.

I realize this amp does not resemble an 18 watt, but as far as pushing the the 5693 with a preceding gain stage, I think it works pretty well. I have the 12AX7 paralleled with a shared 100k plate load and a shared red LED bypassed with a .1uF greenie providing 1.6 volts on the cathode. The supply voltage varies somewhat dependent upon VVR settings. I have played some with tone controls, but currently I am only using a switch to add a .001uF cap in series with the shared .01uF coupling cap. I have a 1M gain pot with a 120pF bright cap, no grid stopper at the 5693. There are no potential dividers other than the gain pot.

I can run the gain pot up full blast at any setting of the VVR or 1M drive pot between the 5693 and the parallel 12AU7 cathodyne PI. No squeals or oscillations and the 5693 can take all the gain the 1st stage has to offer and still sounds great and musical--at least to my ear. In fact, it doesn't really ever get too saturated.
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StarGeezers
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Post by StarGeezers »

Wow Brew, That Must sound really NICE !!! 8) 8) 8)

Guess in the end this is just another 18 watt amp with a Pentode gain stage ... which seems to work out very nicely .... Fender used them , Vox too, I dunno’ if Marshall ever did ? .... Curious ??? Wonder if there are any old Marshalls around with a pentode front end ??? :?:
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Post by zaphod_phil »

I can't think of any authentic Marshall with a pentode gain stage. But a pentode front end sounds fantastic with a regular Marshall 18W type amp.
I realize this amp does not resemble an 18 watt, but as far as pushing the the 5693 with a preceding gain stage, I think it works pretty well. I have the 12AX7 paralleled with a shared 100k plate load and a shared red LED bypassed with a .1uF greenie providing 1.6 volts on the cathode. The supply voltage varies somewhat dependent upon VVR settings. I have played some with tone controls, but currently I am only using a switch to add a .001uF cap in series with the shared .01uF coupling cap. I have a 1M gain pot with a 120pF bright cap, no grid stopper at the 5693. There are no potential dividers other than the gain pot.
Then it's high time you built an EF86 Lite or 5693 Lite 18W!!! And let's please keep the discussions on-topic for this site.
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brewdude
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Post by brewdude »

zaphod_phil wrote:I can't think of any authentic Marshall with a pentode gain stage. But a pentode front end sounds fantastic with a regular Marshall 18W type amp.
I realize this amp does not resemble an 18 watt, but as far as pushing the the 5693 with a preceding gain stage, I think it works pretty well. I have the 12AX7 paralleled with a shared 100k plate load and a shared red LED bypassed with a .1uF greenie providing 1.6 volts on the cathode. The supply voltage varies somewhat dependent upon VVR settings. I have played some with tone controls, but currently I am only using a switch to add a .001uF cap in series with the shared .01uF coupling cap. I have a 1M gain pot with a 120pF bright cap, no grid stopper at the 5693. There are no potential dividers other than the gain pot.
Then it's high time you built an EF86 Lite or 5693 Lite 18W!!! And let's please keep the discussions on-topic for this site.
ZP, that is a pretty reasonable suggestion. I was only trying to add my observations with a triode preceding a pentode. I felt that I should qualify my experience with some design particulars.
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StarGeezers
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Re: 6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimu

Post by StarGeezers »

For those wanting to further discuss this rather “not exactly a Marshall amp “ :roll: ... Please be so good as to join us here ... http://www.wattkins.com/node/17874"
Don’t want to clutter the newly refreshed 18W site up with any non Marshall 18 W babble ... :o

So long , and thanks for all the fish .....
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Re: 6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum

Post by Cyberhorse »

Can I please get the schematic for this amp. Sounds very interesting.
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Daviedawg
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Re: 6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum

Post by Daviedawg »

It is likely that you will have to join Wattkins.com (link on left) and search for it or ask for it. Lots of useful other stuff there.

Dd
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