SoLow Watt 12A_7

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MCK
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Re: SoLow Watt 12A_7

Post by MCK »

Nice tones from that amp and guitar. Great playing and building. What a well rounded musician.
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rdjones
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Re: SoLow Watt 12A_7

Post by rdjones »

What's the equivalent type, a 6BM8?

rd
ampgeek
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Re: SoLow Watt 12A_7

Post by ampgeek »

Looks to be a 6DX8 according to the Duncan TDSL.

http://tdsl.duncanamps.com/show.php?des=ECL84

Interesting that the description says that the pentode G3 is connected to the triode cathode. But....the picture shows it connected to the pentode cathode.

Wonder which is correct? Hopefully Jeff will let us know.

Cheers,
Dave O.
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LeftyStrat
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Re: SoLow Watt 12A_7

Post by LeftyStrat »

ampgeek wrote:Looks to be a 6DX8 according to the Duncan TDSL.

http://tdsl.duncanamps.com/show.php?des=ECL84

Interesting that the description says that the pentode G3 is connected to the triode cathode. But....the picture shows it connected to the pentode cathode.

Wonder which is correct? Hopefully Jeff will let us know.

Cheers,
Dave O.
Looking at a different DS:


1: Triode grid, 2: Triode plate, 3: Triode cathode, 4,5: Heater

6: Pentode plate, 7: Pentode cathode and supressor, 8: Pentode grid, 9: Pentode screen

Pin 7 is also intersystem screen
It's never too late to have a happy childhood.
10thTx
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Re: SoLow Watt 12A_7

Post by 10thTx »

Mine is hooked up with pin 3 being triode cathode & pin 7 being pentode cathode as LeftyStrat stated.

With respect, 10thtx
passfan
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Re: SoLow Watt 12A_7

Post by passfan »

10thTx wrote:You may need a 5Y3GT rectifier and then drop a few volts using a VVR or a zener to not exceed the max ratings.

Although, I would guess you'd be OK and end up with maybe 297v on the ECL84 plates?

with respect, 10thtx
On second glance, my tubes are ECL86's. That's why hammond used a higher voltage. I'm going to give it a go with the (presumably , without checking a datasheet) bigger tubes. Just have to recalc bias and adjust the dropping string and such.
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10thTx
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Re: SoLow Watt 12A_7

Post by 10thTx »

ECL86 = 6GW8

Bogen made an amp using the 6GW8 tube.


And a conversion of that amp showing the ECL86 power amp. Schematic attached.


If you build it, please share how it turns out and a soundclip if possible.

With respect, 10thtx
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passfan
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Re: SoLow Watt 12A_7

Post by passfan »

Will do. Here is what I am starting from. I have some blank chassis on the way now.
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10thTx
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Re: SoLow Watt 12A_7

Post by 10thTx »

Given the two schematics of the 6GW8, I think this would be a reasonable starting place to try this build with an ECL86.

The attached SCH schematic is editable and you can edit the previously posted layout information to match it.

(editable layout is here: http://www.el34world.com/Forum/index.php?topic=13438.0)

I am guessing from the schematics that the 6GW8/ECL86 pentodes are NOT as easily driven into overdrive as the ECL84? So in light of that guess, I changed some of the values between the LTPI and the pentodes to what might be more appropriate for your build.

With respect, 10thtx
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surfsup
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Re: SoLow Watt 12A_7

Post by surfsup »

Thanks for the nice remark.

I build my own guitars. Tele with hollow body and no f-holes.


You play great, you build nice amps, you whip up sweet guitars, sigh...are you one of those kids in "weird science" who built their own woman too? I heard that movie was based on a true story. :wink:
10thTx
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Re: SoLow Watt 12A_7

Post by 10thTx »

You play great, you build nice amps, you whip up sweet guitars, sigh...are you one of those kids in "weird science" who built their own woman too? I heard that movie was based on a true story
The guitars and amps are nice, IMO. My playing seems pretty mediocre on a good day. I've got quite a few friends and a son that smoke my playing easily.

I've probably had people think I am an odd duck. And music is just one of many hobbies I enjoy.

Honestly, my beautiful wife wonderfully exceeds anything I could've ever dreamed up! Very happily married to an incredible woman.
:D

with respect, 10thtx
Tone Lover
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Re: SoLow Watt 12A_7

Post by Tone Lover »

10thTx wrote:
You play great, you build nice amps, you whip up sweet guitars, sigh...are you one of those kids in "weird science" who built their own woman too? I heard that movie was based on a true story
The guitars and amps are nice, IMO. My playing seems pretty mediocre on a good day. I've got quite a few friends and a son that smoke my playing easily.

I've probably had people think I am an odd duck. And music is just one of many hobbies I enjoy.

Honestly, my beautiful wife wonderfully exceeds anything I could've ever dreamed up! Very happily married to an incredible woman.
:D

with respect, 10thtx
Ive been lucky enough to be blessed in the same way heres to having an incredible woman in your life .
with respect.
Bill
10thTx
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Re: SoLow Watt 12A_7

Post by 10thTx »

This SoLow Watt 12A_7 is proving to be a reasonably versatile amp. The cleaner tone has the volume at about 3-4 and PPIMV around 7.
The overdriven tone has the volume about 7 and the PPIMV around 5.5.

Compare this cleaner tone:

http://www.soundclick.com/player/single ... i&newref=1

to the more overdriven tone later in this soundclip:

http://www.soundclick.com/player/single ... i&newref=1

With respect, 10thtx
passfan
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Re: SoLow Watt 12A_7

Post by passfan »

As promised , and finally done enough to post pics and clips...a SoLowWatt with an ECL86 output section. Transformers and output tubes were scavenged from a Hammond AO-44 reverb amp and built from 10thTx's supplied schematic which was modified slightly here and there to suit what I had in the box. The only major mod was the omission of the 470k across the preamp volume pot wiper to ground. I had absolutely no gain control whatsoever and the gain was maxed out at full until it's removal. I will also have to do something about the tone stack as the response, if at all, is slight.

Voltages are as follows:
B+ - 368
B1 - 354
B2 - 281
B3 - 256

V1 plate - 142
V2 plate - 96.7
V3 triode plate - 217
V4 triode plate - 190

Output bias - 11.6

I am going to have to do something about my output bias as It's a bit high right now . I think this amp simply smokes with my cheap old tele. I used an EV n/d 408B cardiod set back about 4' from a crate 4-12 bottom cab with two of the crate OEM drivers disconnected. The sound is more ambient and truer to what you'd hear than if I'd have close miced the cabinet. You may hear some foot taps and background noise and the ditty is something I just threw together and went with for the sample.
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Last edited by passfan on Wed Apr 04, 2012 3:52 pm, edited 1 time in total.
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passfan
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Re: SoLow Watt 12A_7

Post by passfan »

One pic of the outside.
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Forrest Gump
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