Hey folks, are there major differences in the 5G4 circuit and the early 6G4 circuit?Would the two still sound similar? I know all amps sound a little different,but generally speaking are these 2 circuits and tone very close? Thanks to all.
I've played brown Supers, and my collector buddy owns a Tweed 1959. For some reason i get along better with the Brown circuit, the classic Tweed sound is just a little too much sizzle for me, although i love the earlier Twins, Pros and Deluxes. I also loved the Tweed Vibrolux, so maybe my buddy's Super isn't indicative of all of those. It's very clean, he got it for peanuts.
I had been wanting to build a 5G_* version for some time, and have built the 6G_* and 6G_a* circuits in the past. They are all different— and of course they have that great Fender sound.
The 5G4's basic preamp and phase inverter circuitry is the same as the 5G5 Pro, 5G7 Bandmaster, the 5G12 Concert, and the 5G13 Vibrasonic.
Of the five 5G_* amps, only the early Super was tube rectified— the rest being solid-state diode rectified that had very high plate voltages hovering around 500v.
The 5G_* amps had a very short-lived preamp circuit with a .01uF tone cap tacked to the bass pot and a 250pF cap tacked to the treble pot. The woody tweed sizzle is not a feature of the recipe of the scratch-built 5G_* amp I made to explore this evolution of Fender amps.
The normal channel's second gain stage plate resistor is 220k (like the guitar channel on the blonde Bassman), which is a little hairier than the trem channel's second gain stage with its 100k plate resistor. The trem channel's 2nd stage triode is further attenuated at its plate because the two-tube trem circuit provides additional gain— which I have found to be too much for the trem circuit to handle without exhibiting non-musical distortion issues during my circuit analysis testing.
I really like the 5G_*'s lower gain trem channel for singing rock and roll, bright rockabilly and it works well for jazz because the sound is full-frequency rich even at low volumes (I lowered the 10k mid-tone resistor tacked to the bass pot to 6k8 and raised the volume pot's bright cap value from 47pF to 100pF in my 5G_* amp.
The 1960-1/2 6G_* preamp circuit is an adaption of the "James" hifi circuit which was coincidentally developed in the Netherlands around the same time in the late 40s or early 50s (I don't remember the exact date). I guess people see that both 5G_* and 6G_* have a .01 cap on the bass pot and assume that the 5G_* and 6G_* are similar circuits, but the two circuit designs have no evolutionary affinity, as the James circuit was developed close to ten years prior to Fender's 5G_* circuit.
In terms of circuit design, the 6G_* amps are much more sophisticated, but very economical in terms of parts. The James circuit has a cleverly-focused mid-range target while treble and bass frequencies vary independently of it. It is relatively clean-toned (as a hifi circuit would tend to be) and lies tonally between the 5G_* and 6G_A* circuits in terms of "hair" and "airiness" potential.
I would never refer to Fender's application of the James circuit as "hifi".
On a side-note, the latter 6G_A* preamp circuit is directly related to the AB763 blackface circuit. After the latter circuit lost the rocket-science four-terminal treble pots, 5-triode tremolo circuit and opted for higher-headroom, lower-gain 12AT7 tubes in the phase inverter, it became the king of clean while Marshall and Vox soldiered on with their wildly popular over-driving iterations of Fender's short-lived late 50s 5F6A and 5F8A Bassman and Twin-Amp production-run that ushered in the coupling of Fender's long-time use of cathode-follower driven tone-stacks and their new use of the long-tail pair phase inverter.
I find ampology a fascinating subject.
In moving to the blackface era's choppy single-tube optical tremolo, Fender was able to abandon the brownface two-tier branched current-filtering power streams that regulated the two sets of cascading voltages to the tube-happy trem circuit and the separate phase inverter+preamp current stream. The new single-path power distribution topology allowed each power-node (screens, phase inverter, trem and reverb) in an ever-lowering voltage current-stream, to arrive at a finely dc-filtered supply for the final power-node feeding the clean-tone Fender preamp stages. The blackface topology used 1/3 less tubes (for trem-only amps) and two less filter caps than the brownface design— and ended an age of tonal and circuit complexity for Fender amps.
So, other ways to think of the comparison:
Tweed has more mids than brown
Tweed has much simpler preamp, so more of a raw "direct thru" sound
Tremolo on the brown super is sublime
Brown amp hits harder on the attack of notes (or sags less)
Ridgeback said: Wonderful and interesting 2nd post deci, thanks. What do you do for an encore? I have a 6G2-A, 6G4-A, and a 6G6-A.
Thank you, Ridgeback!
I've built and compared the 6G6 series amp's (guitar channel) circuits too. My 6G6-B's effect channel is the same as a 6G4/6G5/6G7-A (among others), so I am able to respond to your comment because I built that amp with switchable solid-state and tube rectifiers.
The main difference between your brown Super and Bassman are about 40v higher at the Bassman guitar channel's plate and a 220k resistor. The Super has 190v and a 100k resistor. The 6G6-A dispenses with the coupling cap (phase inverter's input) as that would've put a dent in the bass channel's resonant frequency— that and it saved Fender the cost of a .001 cap. Also, the Bassman's rectifier is solid state (faster response and higher voltage/higher headroom) as opposed to the Super's GZ34 (5AR4) tube rectifier that contributes a lot to its signature tone.
The transformers (especially the OT) are different for sure. I have not played that amp through its tube rectifier for some time, since I have really been digging the 6G6 Bassman and Super/Pro/Bandmaster-style preamp circuits with the solid-state rectifier because I switch between Brian Setzer and The Cramps mostly using that amp.
I'm not sure which tweed circuit is most similar to your brown Princeton— you might want to compare the 5G11 Vibrolux (also with a 10" speaker) to the 6G2-A.