Bass amp ideas, Odyssey, Winterland etc.

Overdrive Special, Steel String Singer, Dumbleland, Odyssey, Winterland, etc. -
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jph118
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Joined: Wed Apr 19, 2017 1:35 pm

Bass amp ideas, Odyssey, Winterland etc.

Post by jph118 » Fri Jan 05, 2018 7:39 pm

Hey guys, getting some ideas together for a 4x6L6 bass amp using Showman chassis & iron that i have on hand... gathering ideas from SVT, Mesa 400, and of course whatever D-style schems I can get my hands on. My initial thoughts were:

Option 1: SVT-style cathodyne PI followed by triode drivers & CFs feeding each pair of 6L6

Option 2: standard LTP PI followed by CF triodes feeding each pair of 6L6

I see the SSS #002 uses a LTP with CFs feeding the grids, and found an Odyssey power amp schem on here with a LTP folowed by CCs driving the grids. Someone mentioned the original Winterland bass amp used a cathodyne/split-load PI followed by drivers, but i can't find that schematic.

Overall, i'm looking to get as much clean, even response from 4x6l6 output as possible, without distortion. Thoughts??

Subjecttochange
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Location: San Diego, CA

Re: Bass amp ideas, Odyssey, Winterland etc.

Post by Subjecttochange » Sat Feb 03, 2018 6:40 pm

I'm actually planning something quite similar. Did you end up deciding which PI/driver configuration to go with?

JD0x0
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Joined: Tue Oct 09, 2007 2:19 am

Re: Bass amp ideas, Odyssey, Winterland etc.

Post by JD0x0 » Sun Feb 04, 2018 4:56 am

Following, because I too am doing something like this (but for guitar) with a 4x 6L6 Fender Super Six. I was thinking Hiwatt style PI with a cathode follower for each PI output
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It's true i've lost my marbles and i cant remember where i put them

jph118
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Re: Bass amp ideas, Odyssey, Winterland etc.

Post by jph118 » Mon Feb 05, 2018 11:01 pm

I ended up really digging the Ampeg V4BH reissue pi/power section, which is a cathodyne split load followed by two 12AU7 driver triodes into 4x6L6 (although I'll likely use Tung-sol 7581A's). Very similar to the Williamson circuit that Dumble got his ideas from.

Front end is based on the Mesa 400, an old favorite of mine for it's gain staging & EQ, and should fit perfectly into this PI/output section. I've also added a cathode follower preamp output directly after the Master Volume that isn't shown here (apologies for the crude artwork, i'll get an updated schem up here very soon)

*those plate resistors on V3 (12AU7 drivers) are single 47k 1Ws, there was some confusion from the official Ampeg schematic that showed optional 5W's along with the 1W in what looked like a parallel circuit.
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Subjecttochange
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Location: San Diego, CA

Re: Bass amp ideas, Odyssey, Winterland etc.

Post by Subjecttochange » Sat Feb 10, 2018 4:45 pm

Nice!

I think i'm going to do something similar using a LTP instead of a cathodyne and the 12au7 driver stage after it as well. Let us know how it goes!

Yerffej
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Joined: Fri Sep 14, 2007 9:03 pm

Re: Bass amp ideas, Odyssey, Winterland etc.

Post by Yerffej » Mon Feb 12, 2018 10:02 pm

I TOO am planning a 4x 6L6GC bass amp build with some salvaged Peavey iron. Did you find a full schematic of the reissue V4B? I'd be interested to compare the preamps with the SVT classic pre I was planning, and that PI/output drawing you posted seems to make more sense than driving the piss out of 6L6's with the svt design for 6x 6550's. used v4's are cheap and easy to come by these days, but this is more fun. Knowing ballpark voltages would help

I'm using some discrete 100mh inductors from a local shop in the pre

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M Fowler
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Location: Moorhead MN

Re: Bass amp ideas, Odyssey, Winterland etc.

Post by M Fowler » Tue Feb 13, 2018 1:14 pm

I used the Fender Bassman 100 on one build to keep things simple and switched from KT88's to 6550 after a year of band use, we like the 6550's better and better suited for this power section/bias.

Using Hammond 378CX 535mA 800vct power transformer and Hammond 1650TA OT 1k9 4/8/16 120w.

Mark
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Aaron
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Re: Bass amp ideas, Odyssey, Winterland etc.

Post by Aaron » Tue Feb 13, 2018 4:16 pm

If you’re after Winterland inspiration, check out the Marshall Major power amp also.

Thanks,
Aaron

mojotom
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Re: Bass amp ideas, Odyssey, Winterland etc.

Post by mojotom » Tue Feb 13, 2018 6:54 pm

I did build a "smaller" version of the Major amp as I got an old one at hand.

It was simple to build regarding power supply and did work nicely (12ax7 and 12AU7).

I will check my notes as my old Major bass model (running only a pair of KT88 for years) got some others values as the schematics I found.

The second tube in the PI act as a plate driver with big capacitors (470n from memory) between driver and output tubes so it was easier to build than a DC driver (regarding power supply and bias) but I supposed a DC coupled cathode follower driver tube(s) might be a better choice for bass.

The Major looked kind of crude compare to the Ampeg V serie but could be an easier to achieve amp as a start.

jph118
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Re: Bass amp ideas, Odyssey, Winterland etc.

Post by jph118 » Wed Feb 14, 2018 5:55 pm

Yerffej wrote:
Mon Feb 12, 2018 10:02 pm
Did you find a full schematic of the reissue V4B?
I did, on the Ampeg/LOUD service site... lets see if this link works: https://supportloudtech.netx.net/loud-p ... gory/15520

jph118
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Re: Bass amp ideas, Odyssey, Winterland etc.

Post by jph118 » Wed Feb 14, 2018 5:58 pm

Aaron wrote:
Tue Feb 13, 2018 4:16 pm
If you’re after Winterland inspiration, check out the Marshall Major power amp also.

Thanks,
Aaron
Thanks Aaron! That PI is d@mn near the same concept, split load into plate drivers. I like it.

I've been gravitating toward cathodyne PI designs for a while now, maybe bc they're not as common and I dig that aspect.

Yerffej
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Re: Bass amp ideas, Odyssey, Winterland etc.

Post by Yerffej » Wed Feb 14, 2018 11:46 pm

jph118 wrote:
Wed Feb 14, 2018 5:55 pm
Yerffej wrote:
Mon Feb 12, 2018 10:02 pm
Did you find a full schematic of the reissue V4B?
I did, on the Ampeg/LOUD service site... lets see if this link works: https://supportloudtech.netx.net/loud-p ... gory/15520
AWESOME, thanks!

jph118
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Joined: Wed Apr 19, 2017 1:35 pm

Re: Bass amp ideas, Odyssey, Winterland etc.

Post by jph118 » Thu Feb 15, 2018 12:50 am

Thought you guys might dig some pics of the build in progress, still waiting on the backordered PT...

Bassamp1.jpg
Bassamp2.jpg
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