experiment build...5F6A-style + 6g6b

[kwijabo]

started a build last week, progessed enough for me to feel ok posting a progress pic. had a tough time fitting all this neatly. spent more time planning than building so far.

first two tubes are for the 5F6a pre-amp, next two are for the 6g6b preamp. plan is to share the power and PI supply caps, but split to separate preamp supply caps.

not sure yet which of the two's PI, feedback, and presence circuits to use, though. and for this i bought a bunch of the mallory M150's to mess around with some values. going to put in 0.1uF in the 6g6b tone stack instead of those 0.22uF. also might start with 0.022uF couplers to the power tubes instead of the 0.1uF's. i've never built either of these circuits so i have no idea how bassy it will sound. i thought by starting with some lower values it woudl be easier to add some in parallel to up them and see the effects quickly. if i like the higher values i can always switch them out to the higher values.

also, the channels will be mixed with the 470k's at the PI. but the 5F6A doesn't have those. so i think where it will diverge from the standard will be i'll use a 12AX7 in V1 instead of the 12AY7 to make up for the lost gain caused by the mixers. will keep this thread going as the build progresses.

thoughts? comments? emotional outbursts?

[mr_hankey]

Have you compared the 5F6A preamp with the 6G6B bass channel? It has the cathode follower tone stack as well. It's not quite as good as the normal channel as it is (it has less bass and more treble for some reason), but I'm sure a few tweaks could fix that.

Good call on decreasing the cap in the tone stack. I mostly have to roll the bass down as far it will go on the normal channel (mind you, I am using it with a 2x15 cab). I haven't played a 5F6A in years, but I don't think you'll have to do any tweaks there (it's pretty good as it is), unless it's to compensate for your power section and speakers.

[kwijabo]

a 'short' 5 months later and i'm done. dont know if anyones interested but here are some pics.

5f6a side is the bright channel preamp only and a 12AX7 instead of a 12AY7. it has what would be the normal channel's pot set to 0 by grounding 270k mixer to ground. it isn't loud by any means, exacerbated by the fact that it again gets mixed later on with the 6g6b preamp channel, so i may get rid of that first divider off the volume pot. but its clean tone sounds great.

only change to the 6g6b pre amp is a 0.005uF across the plate resistor where it calls for a 0.002. this channel is b-r-ight and the higher cap seems to make it more useful.

the feedback / presence is the 6g6b circuit. the coupling caps between the p.i. and power tubes are 0.022uF. like them better than 0.1uF here.

i got transformers for a deluxe reverb build but decided to scrap that project and make this instead. so this is actually running 6V6's and deluxe reverb PT/OT/choke.

it makes a really nice house amp, especially the 5f6a circuit because it sounds good and isn't that loud. but i took it out to a gig last weekend and that channel had some trouble cutting through the mix, even at loud settings - it just seemed muddled. the 6g6b preamp channel cut through better.

[Structo]

Nice looking build.

Have you used the Jupiter caps before?

[Milkmansound]

nice looking work!

I love those Jupiter caps - been using them exclusively since I first tried them about 3 years ago.

[kwijabo]

yeah i used them in my last build that had a pretty high gain channel. between that build and this one i've had no problems with them and they sound fine. i haven't A/B'ed them in the same circuit with any other brand to compare so i don't know their exact impact, but they certainly don't sound bad. good enough that i'll be using them in my next build, too. they are bigger than the mallory 150's and quite a bit more expensive relative to most of the other caps. but if those factors don't deter you i would give them my recommendation.

[Blackburn]

That's a good looking build. I used few Jupes a while back and have been wanting to use the red ones in some upcoming tweed stuff. What speakers/cabs have you been liking with this build?

[Bob S]

Nice build - you used some good stuff in there.
Are they ceramic caps on the IEC inlet ?

[kwijabo]

speakers - i have two cabs. a 1x12 vintage 30 pine, and a 2x12 carvin with the carvin gt12's. both are open back, and i like the 1x12 more. but i took the 2x12 out to the gig with it since it is more durable.

those are MOV's, not caps. they should (probably? maybe?) be on the other side of the switch. but i was trying to fit a lot in that chassis and it tested my layout skills so i just put them right on the IEC thing. i followed the suggestions Premier Guitar's "Immortal Amp Mod's" regarding putting diodes in series with the tube rec (they are shrink wrapped and you probably can't see them in any of the pics i posted) and MOV's. they're also what you see on the output transformer / power tube plates on that 4-turret stand alone strip, but different values. i hadn't used them like that before.

http://www.premierguitar.com/articles/t ... fier-mod-1
http://www.premierguitar.com/articles/t ... ods-pt-3-1

(i came across those articles from this post. leadfoot did a nice job incorporating them into an express: https://tubeamparchive.com/viewtopic.ph ... sc&start=0)

you can usually tell what time of day i purchased parts for an amp based on their price: late at night = willing to spend more. and for a while i was really into trying to make a great deluxe reverb and thought maybe the MM fat stack was the way to go. that's why i had the transformers. they certainly don't sound bad, but i have nothing to compare them against since i've never built this circuit before nor swapped anything.

[dannyreckless]

Do you have any sounds samples of the 6g6b side?
curious how it sounds with the 6V6 power section.

[Structo]

yeah i used them in my last build that had a pretty high gain channel. between that build and this one i've had no problems with them and they sound fine.

The Jupiters seem to have a following but a guy I know who runs a parts website said they changed them not long after they were marketed.

He claimed they were nowhere near the quality or 'tone' of the original.

I don't mean to dump on the Jupiters and if you like them, nothing to worry about.

[kwijabo]

i don't have any sound clips - maybe a weekend activity? i don't really have a good recording setup but maybe enough to give a rough idea.

re the jupiters...i've used them in a few builds. they are fine. i recently rebuilt my liverpool with them instead of 6ps OD's. honestly, some may be able to notice the difference but i can't tell exactly what difference they are making. other things like voltages, actual R and C value changes, and speaker choice make way more of a difference. though i do like that i don't have to worry about outer foil orientation with them.

thanks for passing on the information. if true its a shame, but not unseen before in the business world.