Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on July 12, 2018, 05:05:29 am

Title: 6GW8 Parallel SE
Post by: TIMBO on July 12, 2018, 05:05:29 am

Hi guys, Looking at doing something simple.

(https://i.imgur.com/cVsayjC.jpg)

Questions...
What OT primary am I needing and what power rating.
 :icon_biggrin:

Title: Re: 6GW8 Parallel SE
Post by: tubenit on July 12, 2018, 06:48:37 am

I like that idea!  You sure come up with some cool stuff!   :thumbsup:

With respect, Tubenit

Title: Re: 6GW8 Parallel SE
Post by: sluckey on July 12, 2018, 06:55:21 am

Do you have a stash of 6GW8s? They are kinda pricey over here. About $60 each.

Title: Re: 6GW8 Parallel SE
Post by: shooter on July 12, 2018, 09:14:34 am

Quote

What OT primary am I needing and what power rating.

need a 2nd opinion, but looks like ~RA 24k, so 1/2 ~10k-ish, so a 5K using a 4ohm skr on 8ohm tap  :dontknow:

power-wise, a low range would be 15W, go up from there

when I get some time i'll try and hunt down a data sheet

Title: Re: 6GW8 Parallel SE
Post by: shooter on July 12, 2018, 11:06:31 am

while rooting around the web I found this paper by your neighbor, might help?  It's PP, but PSE specs should be "close enough"

https://dalmura.com.au/static/Australian%206GW8%20PP%20amp.pdf

Title: Re: 6GW8 Parallel SE
Post by: tubeswell on July 12, 2018, 11:19:23 am

Quote from: shooter on July 12, 2018, 09:14:34 am

Quote

What OT primary am I needing and what power rating.

need a 2nd opinion, but looks like ~RA 24k, so 1/2 ~10k-ish, so a 5K using a 4ohm skr on 8ohm tap  :dontknow:

Yes - the pentodes are rated at 9W. For centre-bias class A, running at (say) 300V:

300/(9/300) = 10,000R.

2 in parallel would be 5k.


As to power rating - figure about 40% of (2 x 9) = 7.2W. 2 or 3 more watts above this would be a good margin of safety ;-)

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 12, 2018, 01:46:54 pm

Thanks guys.

Sluckey, I have a few 6GW8s left, but my supplier has a stack of 14GW8s

He's looking to get some transformers wound to accommodate the 14.5v heaters.

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 14, 2018, 05:27:29 pm

(https://i.imgur.com/HN7DKls.jpg)
The reverb will be a work in progress, as the Belton brick is something I want to try.
After rummaging through my discarded builds I was able to find a few bits I could use.
(https://i.imgur.com/XO1qMco.jpg)
(https://i.imgur.com/pmieeeu.jpg)
The chassis has been sitting on the shelf for so long I can't remember why I had it bent like that. :dontknow:
WASTE NOT WANT NOT
(https://i.imgur.com/xcVYnXn.jpg)
(https://i.imgur.com/PSLkf84.jpg)
 :icon_biggrin:

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 18, 2018, 05:55:53 am

Hi guys, Some progress.....
(https://i.imgur.com/s5knxYL.jpg)
(https://i.imgur.com/1sRcFqO.jpg)
(https://i.imgur.com/jflJKw0.jpg)
(https://i.imgur.com/8emyzvx.jpg)
(https://i.imgur.com/dOgUvdk.jpg)
Just waiting on the OT

Title: Re: 6GW8 Parallel SE
Post by: kagliostro on July 19, 2018, 04:28:10 am

 :thumbsup:

Franco

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 20, 2018, 03:53:41 am

Thanks Franco.
Guys I had another think about the heater supply.
I using a 1A transformer that ahs 6.3v and 12.6 taps and I will be adding a 12AX7 to the 6GW8.
(https://i.imgur.com/WOUR377.jpg)
Would this be a better circuit.

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 21, 2018, 04:58:12 am

Hi guys, Tweaked the circuit some and fired up well, sorta.

The back to back transformers under load did not have the expected 300ish output  :crying:
A bit of head scratching and connecting the 18v tap on the first transformer to the 12v tap on the second transformer helped greatly.

Still not quite 300v but good enough.
(https://i.imgur.com/4OYashO.jpg)
(https://i.imgur.com/SJ7AjyL.jpg)

Title: Re: 6GW8 Parallel SE
Post by: tubenit on July 21, 2018, 08:45:10 am

Timbo,

As always, thanks for sharing your info and schematic!   

How does it sound?

with respect, Tubenit

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 21, 2018, 09:31:28 pm

Thanks T, This little amp sounds like a BIG amp.
Had a muso give it a whirl and I was very impressed.

Plenty sparkle and great bottom end.

Would work well with 6BM8s

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on August 08, 2018, 05:09:48 am

Hi guys, After much tinkering I think I've got this one done.
Adding the Belton reverb brick was a bigger job than I thought.

If you like plenty of reverb these bricks are great and sound pretty good.

I need to do some tiding up and I'll get some pics.
(https://i.imgur.com/AxXq7dk.jpg)

If there is anything I should not have done please tell me, as it was very much trial and error addon.

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on August 09, 2018, 05:08:45 am

Hi guys, put the finishing touches on the circuit.
(https://i.imgur.com/QT8FQFN.jpg)
(https://i.imgur.com/ZqlwEvB.jpg)
(https://i.imgur.com/1IijfYP.jpg)
(https://i.imgur.com/vWLCqdH.jpg)
(https://i.imgur.com/rdIbE19.jpg)
(https://i.imgur.com/qYN39H6.jpg)
(https://i.imgur.com/1KYP41N.jpg)
Overall I think this one has turned out pretty good.
Does clean to mean very well with great reverb.
Cab is under construction as we speak.

Title: Re: 6GW8 Parallel SE
Post by: uki on August 14, 2018, 09:40:51 pm

Sound sample pls ?!  :icon_biggrin:

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on August 15, 2018, 01:46:51 am

Will do ASAP.

Title: Re: 6GW8 Parallel SE
Post by: TIMBO on July 11, 2020, 05:57:37 pm

Hi guys, The "CHICKABOO 10" is complete.
(https://i.imgur.com/fbcFKkb.jpg)
(https://i.imgur.com/ZvhQI0o.jpg)
(https://i.imgur.com/qS7BUOb.jpg)
(https://i.imgur.com/w5fx2DN.jpg)
(https://i.imgur.com/3y87cAv.jpg)
Will work on some clips soon.

Title: Re: 6GW8 Parallel SE
Post by: shooter on July 11, 2020, 06:41:14 pm

true craftsmanship! 

nicely done

Title: Re: 6GW8 Parallel SE
Post by: bmccowan on July 11, 2020, 08:49:41 pm

Super nice! I'll be interested to hear some sound clips. Parallel SE amps have their own charm.