5F4 Tweed Super Mod Build--Shorting with Power Tubes

[Stevem]

A 6L6G is only a 19 watt tube, not a 30 watt like your running now, so watch how you bias those in!

[pdf64]

A 6L6G is only a 19 watt tube, not a 30 watt like your running now, so watch how you bias those in!

It’s not valid to directly compare design centre rated anodes to those of design max rated types.

[ViperDoc]

I found a document that records original Fender transformer model numbers and output impedances. See here: http://www.bustedgear.com/res_Fender_ou ... ormers.htm

I was unsure about the Fender 45216 OT impedance rating as most current reproductions (like mine) have multi-tap secondaries. It appears the 45216 OT was a 4-ohm secondary output impedance.

This came in handy when deciding final GNFB resistor values.

[pompeiisneaks]

I found a document that records original Fender transformer model numbers and output impedances. See here: http://www.bustedgear.com/res_Fender_ou ... ormers.htm

I was unsure about the Fender 45216 OT impedance rating as most current reproductions (like mine) have multi-tap secondaries. It appears the 45216 OT was a 4-ohm secondary output impedance.

This came in handy when deciding final GNFB resistor values.

I really liked this info, and since we often end up with dead links, thought I'd link to it and screenshot the data here:

https://ampgarage.com/forum/viewtopic.php?f=8&t=34439

~Phil

[ViperDoc]

I have a question regarding this E-Series EQ in the 5F4 circuit.

As an update, I recently made some finishing touches on this build, still in the midst of others:

1) Changed the LNFB switchable value from a 0-5K pot to a 4M7 + 5K pot to allow for a lower custom LNFB setting, currently at 8K5 and sounding dynamite with a Strat.
2) Installed a bias switch to enable proper bias resistance for 6L6G tubes, currently running the 6L6Gs at around 29-30 mA cathode current. The lower running tube runs 2mA lower.
3) lowered the PI output caps to .022 uF after dealing with unexpected bass, even out of an open back 210 cab.
4) To that end, I also installed a 1M pot in series with the 470K PI grid stopper I originally installed to further swat down the flub.

My question is this:

Generally, the amp is dead quiet, sounds great at the right settings with the right guitar and all that. I hear a hole in mids on this amp however. It has more quack than I hear in the 5E3. The overdrive texture and transition are quite different also, more glassy I would say, and harsher. Obviously a different beast. I played around with an online tone stack calculator but couldn't seem to make sense of how I'd change the values.

As a note, while making changes, I briefly added a second parallel 16 uF eCap on Node A to bring the filtering to 32 uF pre-choke, but didn't add another after the choke (Node B for Screens). I actually really liked it until I turned it up--it had way too much hair on it. I know the 5U4G rectifier is "good" for 40 uF or cap input, but couldn't find good info on whether you should keep both C values the same on both sides of a choke.

If you have any thoughts, I'd appreciate them as always.

Here's a current schematic:

VIPERDOC 5F4 SUPER SCH 1.7.pdf

[pdf64]

I found a document that records original Fender transformer model numbers and output impedances. See here: http://www.bustedgear.com/res_Fender_ou ... ormers.htm

I was unsure about the Fender 45216 OT impedance rating as most current reproductions (like mine) have multi-tap secondaries. It appears the 45216 OT was a 4-ohm secondary output impedance.

This came in handy when deciding final GNFB resistor values.

I really liked this info, and since we often end up with dead links, thought I'd link to it and screenshot the data here:

https://ampgarage.com/forum/viewtopic.php?f=8&t=34439

~Phil

That bustedgear info is incorrect in regard of a CT on an 8ohm secondary providing a 4ohm tap.
A CT would reflect 1/4 the impedance back to the primary, ie in the above case, it would be a 2ohm tap.
I think all the references to secondary CTs are probably incorrect, that’s certainly the case for the late 70s / early 80s models. ie they weren’t actually CTs. The secondary taps were for half impedance, not 1/4.

[ViperDoc]

I found a document that records original Fender transformer model numbers and output impedances. See here: http://www.bustedgear.com/res_Fender_ou ... ormers.htm

I was unsure about the Fender 45216 OT impedance rating as most current reproductions (like mine) have multi-tap secondaries. It appears the 45216 OT was a 4-ohm secondary output impedance.

This came in handy when deciding final GNFB resistor values.

I really liked this info, and since we often end up with dead links, thought I'd link to it and screenshot the data here:

https://ampgarage.com/forum/viewtopic.php?f=8&t=34439

~Phil

That bustedgear info is incorrect in regard of a CT on an 8ohm secondary providing a 4ohm tap.
A CT would reflect 1/4 the impedance back to the primary, ie in the above case, it would be a 2ohm tap.
I think all the references to secondary CTs are probably incorrect, that’s certainly the case for the late 70s / early 80s models. ie they weren’t actually CTs. The secondary taps were for half impedance, not 1/4.

I never noticed that before, doesn't make much sense. Thanks for noticing that.