5F6H
455 posts
Dec 29, 2010
3:39 AM
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@ Harpboy - +1for Watfordvalves. If your amp is fixed bias then it is advisable to have the power tube's bias current checked when these are replaced. For current production amps Watford & Hotrox do pre selected power tube "kits" designed to "drop in"& run within resonable perameters.
Be aware that some brands of power tube run vastly different bias currents, enough to blow things like rectifiers if just slapped in...so speak to whoever you buy from, don't just go by the fact that some said they tried a certain brand in another amp and they were great.
If changing power tubes is something that you are likely to want to experiment with then buy some bias probes, they pay for themselves after a short while.
All 12A#7 preamp tubes can be considered as interchangeable, inc. 5751.
ToddG - Almost everyone who runs brown Concerts runs 12AX7 in V1-V5, R to L, (I like the JJ ECC83S), usually V6 too but 5751 & 12DW7 can work well here. Another common trick with these amps is to remove V2-V5, just leaving in V1 & the phase inverter(next to the power tubes) this gives a hotter, tweedier tone. I prefer to keep all the tubes in place, if you plug into the normal channel, the unused controls on the Vibrato channel still affect your tone, run vol & bass full up, then you get an additional high boost from the treble control.
V3 & V4 (from R to left) work the vibrato, V5 mixes the vibrato in to the vibrato channel. V6 sends the signal for both channels to the power tubes.
Brown concerts run pretty high plate voltages, some brands of tube will also run very high idle currents...so I would look at this to reduce feedback, more than the preamp tubes, my "go to" tube in this amp is usually the Sovtek5881WXT, or Phillips6L6WGB but you normally need to rebias with NOS tubes. A loud, properly functioning Concert might hit feedback at anywhere between 2.5 & 4 on the dial with a stock 1MA volume pot...this can be adjusted however, for a more useful sweep, but means some soldering.
I wouldn't really recommend a 12AU7 in V6, it dissipates a lot of Wattage and can kill the plate resistors (again due to high voltages in the Concert).
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