looking to add tremolo to overbuilt amp:

[dansamp]

a friend owns this amp and is wanting to add tremolo to it;

it is a Matchless DC 30 that was converted to octal pre-amp tubes
by Overbuilt
anyway I am thinking about adding a Deluxe 6G3 type tremolo to it
using the empty tube socket near the front panel

not sure how that would translate from a fixed bias power tubes
to cathode biased tubes
any advise would be greatly appreciated;
I am attaching gut shots for your viewing pleasure

Thanks in advance

[wyatt]

I don't think the 6G3 trem will work, it varies the fixed bias of the power tubes.

But if you go to the 5E9 Tremolux (which is cathode bias, unlike the later 5G9), it varies the PI bias, here is a schematic...

[Phil_S]

Read this, save yourself some trouble installing a tube for no good reason: http://www.geofex.com/Article_Folders/s ... remolo.htm

Look at the Gibson Scout GA17-RVT, Explorer GA15-RVT, and Minuteman GA20-RVT for examples of cathode biased PP amps with tremolo. BTW, the Explorer and Minuteman both use an incandescent optocoupler that isn't available. I listed those so you can see where to insert the return. The Scout doesn't have one.

Edit: LOL! While posting, I see the Tremolux came up. I forgot about that one. Great tremolo on that amp.

[jjman]

You can use the 6g3 approach on a cathode biased output pair by connecting the intensity pot to ground instead of to the bias circuit. Either way that outer lug of the intensity pot is at ac ground. You need that outer lug at ac ground so the ac/signal current from the PI can flow thru the 220k grid leaks and on to ground.

[dansamp]

You can use the 6g3 approach on a cathode biased output pair by connecting the intensity pot to ground instead of to the bias circuit. Either way that outer lug of the intensity pot is at ac ground. You need that outer lug at ac ground so the ac/signal current from the PI can flow thru the 220k grid leaks and on to ground.

Great !!!!

thanks for that .

now I don't know which would be better
the 6G3 or the 5E9A ......

[jjman]

5e9a trem uses 2 triode sections and 6g3 only one. 5e9a intensity control will affect the dc bias of the PI as well as the trem strength. Just like the Vibro Champ does, even when switched off. If you removed the trem tube from 5e9a, the PI's bias would be affected since the trem tube pulls its 2nd cathode thru the same path.

2-triode types use the cathode of the 2nd one as the trem's "output." More stamina from the lower impedance when tapping there for sending trem voltage to output grid-leaks.

5e9 uses the more rare PI (paraphase ?) instead of the LTPI. Not sure if that's important or related to the way it's trem is implemented thru the PI's cathode path. I guess that trem could be placed on a LTPI. If NFB is in the vicinity things might get difficult. 6g3 and 5e9a have no NFB.

I used the 6G9-B trem on my cathode biased 6v6 outputs homebrew. Also have a Harmony H415 with a small pentode trem tube and similar insertion approach. Outer intensity lug to ground since no negative DC bias circuit to connect to.

http://www.el34world.com/charts/Schemat ... ny_415.pdf

Default is “On” with the Harmony and 6g9b which I reconfigured to “Off.” Either default can be implemented on these non-roachers. However I find the “Off” default approach does not allow for quick trem turn-on. Not a problem for me. GA19RVT uses this “Off” default via switching the ground of the speed pot.

http://www.el34world.com/charts/Schemat ... -19RVT.pdf

“On” default approach usually grounds “off” the oscillation cap-string via its switch.

[dansamp]

jjman,
thanks for all the info

the amp I have is basically an AC30 circuit , so no NFB

I think I will try the 6G9 since it seems to be more simple

again thanks everyone

Dan.