The plate coupling cap on the line amp seems quite low ? Won't this roll off lfreq significantly ?
I use around 1uF in my redd style line amps usually, and even higher in other parafeed line amps.
Also, the preamp plate caps seem similarly a bit low to me, although I guess it's part of the ampeg b15 signature sound.
And 450K plate load on the sl7 seems very high. Great for psrr though! I mostly like to to run a 6sl7 with a decent amount of current, and 150K or so plate load max.
The only time I've used 470K plate load has been with ax7 in a hifi integrated amp's preamp section, that had a lot of nfb into the cathode. It really needed that extra bit of gain to cater for phono/riaa/nab curve stuff.
Notwithstanding, I'm sure the ampeg guys had their reasons ... no disrespect meant!
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Interested in how it all shapes and measures up .... I'm reworking my own 'tube amp + line stage' build to really hammer hum down as far as I can, given the modest amount of chassis space.
I have about 2/3 of the area of a 19" rack and keeping sensitives away from high amplitudes is challenging - some heroics required ... better seperation of wiring, and for the preamp/lineamp, a second, high L choke (Hammond 157G 30H@40mA) plus dc heaters to boot.
I tend to overdo it on R-C psu filtering stages - I'm going for a pair of 3-section JJ electro caps for my rework. Something like 120uF total for the power amp and around 270uF total for the other stages.
As always, it's that last couple of dBs of noise performance (eg. 3 to 4 dB or so) which is hardest to achieve, and delivers the difference between 'working' and 'inspiring'.
I'm using a utc a-44 traffo with the optional shield, and it still picks up hum pretty good. One has to get the right utc orientation to even stand a chance of good performance . If I would redo the money, it would be some mu-metal canned Sowters!
Even after all that effort, to try to achieve something approaching 80dB of signal-hum for the line amp, at +4 dBu nominal, with a happy +12dB or so of headroom ... when the power section is doing 10Wrms or so ... I still use a gate-compressor 1ru unit off the line amp ..... to really get where I want to be ... guitar amp recording fidelity wise ;D
For cheaps, I like the ART TCS unit! A few dinares more for a dbx 1066 would be a worthwhile refinement. I used to use my Ymaha 03D digital mixer for it's excellent 'compander' section to similar effect. Ultimate gate imho is the TC Finalizer+ .. which I have on the main mix bus 8)
I *am* finding that modern gate plug-ins are really starting to shine .. for use 'after-the-performance' - like the Eventide gate plug, or the SSL native or TeamDNR's MixControlPlus channel strip plugs.
A good, low noise feed provides that extra bit of long duration, low dB 'tail' for downstream gates to work with.
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The combination of low-ish power (10 to 15W) tube combo with a great line stage is dynamite in a 'recording' context - its really thrilling to capture a true-to-life sounding feed of the amp and re-inforcing that thru the monitor/fx/record chain, to really fill a room at reasonable volumes .. where 'lounge room' style tracking captures the most inspired performances.
I like to run a few mics as well .. for blending options inside Cubase
Pure luxury 8) 8)