18 watt Selmer Zodiac

Post by **zaphod_phil** » Tue 12/19/06 11:38 am

Crock skin tolex with oversized gothic logo - it doesn't get much cheesier than that! Still neither's too hard to fix - or else if I bought one I could always sell the cab off to ChrisU.

PeterS · Post by **PeterS** » Thu 12/21/06 1:59 pm

it doesn't get much cheesier than that!

You say that like it's a BAD thing!

Post by **zaphod_phil** » Thu 12/21/06 2:52 pm

How did you guess?

Post by **markh** » Thu 12/21/06 5:43 pm

Here's a better (but still not perfect) schematic.

EM84 -- now that's a cool tube!

--mark

Post by **zaphod_phil** » Thu 12/21/06 5:48 pm

It's a pity they only used it with the tremolo oscillator. Would have made a real neat VuMeter.

rjguitars · Post by **rjguitars** » Sun 01/07/07 12:15 am

Hey Guys,

I was just watching a "CREAM" historical video tonight. I noticed that Clapton was using SELMERS in all the early photos of him... songs like "White Room", Sunshine of Your Love... it was great stuff.

rj

Snapcase · Post by **Snapcase** » Thu 02/18/10 7:51 am

Any idea of the OT primary impedance used for these circa 30W Selmers?

These models (Zodiac 30 and Selectortone Automatic 25) have a plate voltage of 445V for 25 or 30 watts respectively. According to the Mullard EL34 spec sheets for a cathode biased AB push pull pair, with such a voltage and Rk=465Ω per tube should put out around 40 watts over a 6K5 load. What they used to get only 25 or 30W? A lower load? Shouldn't that approach distort quite early? Those are supposed to be rather clean amps if not pushed... If I'm not wrong.

StarGeezers · Post by **StarGeezers** » Thu 02/18/10 9:01 am

If you're talking about sweet Tone , ZP called it !!! Pentodes in the pre amp!!!

Extensive experimentation at Sewatt and Wattkins , has produced unusually sweet sounding amps , all with Pentodes in the Preamp !

Snapcase · Post by **Snapcase** » Thu 02/18/10 11:07 am

Pentode gain stages were very common in late '50s and early '60s audio amps. Sadly they are almost forgotten due to the huge influence of the two big names brands. Every player wanted an amp with a big F or a big M on it, perhaps with the only exception of Vox due to the fab four fame.

If you look for old european amps schematics, both Hi-Fi and instrumental, you'll find plenty of interesting pentode preamp ideas to try.

About the Selmer thing, I still have no clear who copied who. Gibson to Selmer or Selmer to Gibson. Just check the GA80 Varitone schems and compare to Selmers. Who did it first?

Snapcase · Post by **Snapcase** » Sat 02/20/10 7:32 am

I think the rules do allow mention of other amps within the context of comparison against Marshall 18Ws.

Oooopss.... sorry.

I'll try these questions anywhere else.

StarGeezers · Post by **StarGeezers** » Sat 02/20/10 9:01 am

At Sewatt and Wattkins, we've been using Pentodes (6U8 , 6SJ7 ) in the preamps , and having great sounding results ... There's just something special that happens with a Pentode ... very Sweet and musical sounding ... very different than the usual 12AX7 ...

Our best results were having a gain stage driving the Pentode >PI> PA

As far as the 18 watt... our Absolute Minimum has just a 6SJ7 driving the PI ... Tons of gain and Killer Tone ... simple amp ...

Snapcase · Post by **Snapcase** » Sat 02/20/10 10:33 am

I'm a huge fan of preamp pentodes. I have an even simpler amp with an EF86 driving two parallel EL84 SE power stage. (no PI obviously) It sounds killer.

All my preferred amps have a pentode driver followed by a split load PI. using an ECF80 or a 7199 for this. Not too far from the Selmer thing. Only simpler with a single pentode instead of pentode second gain stage in each channel before the PI. This is why these Selmers appeal me hugely too.

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18 watt Selmer Zodiac

Claptons early choice was Selmer...