..asking help to get more sag/compression 6v6's

puddlefish

Member
Messages
190
I'm wondering if there' a small mod or two that can get me more tactile/spongey feel from the power section.Even though the filter caps are smallish it's not getting as spongey as I'd like.I have a 5y3 rectifier in there.

the amp's schematic is virtually identical to this one,except:

*the 6v6 cathode resistor value is 300 ohms instead of 200 ohm

*there is no field coil speaker but rather a coil/choke in it's place and I have a 20w watt alnico Weber Blue Pup(which break up nicely)

*the 6SC7 is actually a 6SL7 (virtually the same tube with same gain factor of 70)

I really dig the amp,it's portable size,the quality,it's cleans-it's grungy crunch at full bore..however the in-between tones sound/feel more like a single ended amp,somewhat stiffer.

Maybe adding a bypass cap to the cathode resistor to work the filtering harder?Can I disconnect one of the filter caps?(are the 6v6s seeing 10uf or 20uf filtering?)How about the gain of the phase inverter,can it be upped?

 

pdf64

Member
Messages
7,364
I suggest you add a HT node for the screen grids, eg as per a 5E3 http://www.fmicassets.com/Damroot/Original/10001/8150500_gamp_schematics.pdf
Such 4k7 HT dropper will introduce a significant degree of sag; currently, depending on the choke resistance, the HT supply to the screen grids may be stiffer than eg a 5E3.
Bypassing the cathode bias resistor will likely decrease compression, but it may be beneficial following the above mod to the screen grid supply.
 

puddlefish

Member
Messages
190
I suggest you add a HT node for the screen grids, eg as per a 5E3 http://www.fmicassets.com/Damroot/Original/10001/8150500_gamp_schematics.pdf
Such 4k7 HT dropper will introduce a significant degree of sag; currently, depending on the choke resistance, the HT supply to the screen grids may be stiffer than eg a 5E3.
Bypassing the cathode bias resistor will likely decrease compression, but it may be beneficial following the above mod to the screen grid supply.

OK thanks,at what junction would I place it?between the OT center tap and the second 10uf cap?
 

pdf64

Member
Messages
7,364
No, the OT CT needs a de-coupling cap; the choke's 2nd terminal, 2nd 10uF cap and OT CT form the HT plate supply node.
Need to add a HT supply node for the screen grids, eg 4k7 and a de-coupling cap of any convenient value, inserted between the plate supply node and 27k HT dropper to the phase splitter.
 

puddlefish

Member
Messages
190
No, the OT CT needs a de-coupling cap; the choke's 2nd terminal, 2nd 10uF cap and OT CT form the HT plate supply node.
Need to add a HT supply node for the screen grids, eg 4k7 and a de-coupling cap of any convenient value, inserted between the plate supply node and 27k HT dropper to the phase splitter.

Thanks.That said please pardon my novice understanding of electronics.I'm upside down on the instructions.

I looked up "decoupling cap" and understand it to be a bypass cap?And the "second terminal" of the choke would be the end that is connected to the OT CT?

Also the connection for the 4k7/& additional de-coupling cap at the "plate supply node" would be the OT Ct no?And when you say "27k HT dropper to the phase splitter" do you mean the connection on it's left side?

FWIIW there is a typo in this schematic,I just looked another one up.The 10uf on the left side is connected to the all the plates in the preamp(6sq7 and both halves of the 6sc7).IE there's a little C shaped overpass shown but instead the schematic should illustrate a connection at that point.
 

Blue Strat

Member
Messages
30,183
If the 5Y3 in use is a Sovtek replace it with a NOS 5Y3. The Sovteks produce a voltage which is too high.

If the suggestions above don't help, try a 100 ohm resistor in series with the B+ node.
 

pdf64

Member
Messages
7,364
I looked up "decoupling cap" and understand it to be a bypass cap?And the "second terminal" of the choke would be the end that is connected to the OT CT?
Yes to both.
the connection for the 4k7/& additional de-coupling cap at the "plate supply node" would be the OT Ct
Yes
And when you say "27k HT dropper to the phase splitter" do you mean the connection on it's left side?
No, the right side.
 

puddlefish

Member
Messages
190
Yes to both.
Yes
No, the right side.

oK,thanks,getting closer..I ask again(because I think there may have been confusion)do I not solder one end of the 4k7 to the junction of of the 27k and middle 10uf cap and the other end to the plate supply node?Doesn't the existing middle 10uf fill the role of the "de-coupling cap of any convenient value" ?..fingers crossed
 

puddlefish

Member
Messages
190
If the 5Y3 in use is a Sovtek replace it with a NOS 5Y3. The Sovteks produce a voltage which is too high.

If the suggestions above don't help, try a 100 ohm resistor in series with the B+ node.
It's a vintage newish old stock 5y3.I think I have a 2w or 5w of similar value lying around,might try that..thanks
 




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