I have an unmodded circiut V18. I have replaced the reverb pan with a new accutronics which is the only mod I’ve made. I’ve swapped a few tubes around but its back to stock now. I just got my hands on a set of real nice vintage RCA 12AX7A’s that I pulled from an old Lowrey organ. The tubes are marked 61-22 274. My question is has anyone tried replacing the stock tubes with vintage RCA’s without doing any other mods? I am curious as to what difference you got with just the tube swap. I’m going to try the swap myself, but I won’t be able to get to it for a couple days so I figured I’d ask and see what others know.

While I’m at it I’m also going to try an old Sound City By Sylvania 12AU7 that is marked H6V 713 and an old RCA 12AT7 that I can’t read any markings on other than Made in USA.

To compare them I’m going to first record the amp with stock tubes. The I’ll swap out something, and record again with the same guitar, same settings on the amp, etc. This way I’ll get an idea of how it sounds while I am playing, plus I can refer back to recordings to compare.

From the tubes I’ve mentioned, which would be your first choices to try? Of course I know the first things you’ll all ask is what kind of sound am I looking for. I play blues, rock and some metal (when I feel like letting out some frustration ) I play mostly at low volume and I like anything from a sweet clean to heavy OD/distortion. I do have pedals I use at times for low volume playing, a Bad Monkey and a Marshall Guv’nor.

I do have the speaker broken in pretty good and it sounds much better now. Also because of the volumes I play at I don’t really have issues with overwhelming bass or boxy tones. I can dial in pretty good tone with it stock at the volumes I play. Of course pretty good means there is room for improvment. I’m staying away from circiut mods for right now so I don’t void the warrenty so soon. I guess if I was playing at louder volumes more mods might be needed, but at the volume I play I can easily get all the clean I want.

For any of you that know me by my posts here, you know I have a ‘73 vibro champ that I love. Last week I was asking some questions about tubes I pulled from an old Lowrey organ. The tubes turned out to be RCA’s that were branded as Lowrey.

There were two 6V6GT’s: On the side they say:

Made in USA
61-22
274

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and three 12AX7A’s also marked:
Made in USA
61-22
274

Anyhow, just for fun, I decided to try them in my Vibro Champ. To do the test I first played the VC with the stock tubes (yes mine still has the original tubes) I played for about 30 minutes on my tele using all three pup swtich settings. I then let the amp cool a bit and changed the preamp and power amp tubes to the "new-old" Lowrey stamped RCA’s. Once again, I fired up the amp and played with the exact same amp settings. The tele was full up on both volume and tone for both sets of tubes. Now mind you, I thought the amp sounded pretty darn good before - but I was blown away by the difference! The RCA’s from the organ sounded incredible! I think the orignal tubes were also RCA’s but all the writing was rubbed off and all I can see is what looks like some where letters once were, the same color ink I see on other old RCA tubes.

The new tone from the amp sounded even more open and alive. More clean headroom and even sweeter tone. Since the old tubes still work fine, I put them on the side in my tube box along with my new "spares" from what was left over from the organ, one 6V6GT and two 12AX7A’s. Not only did I find my tone, but I have extras of the tubes that made it happen.

Fender made the blackface bassman amp between 1964-1967. The bassman was designed as a bass amp but very quickly became a favorite of many guitar players. I’ve read that the original Marshall amps were designed based on the Fender Bassman circuit. The Blackface bassman was designed as a piggy back setup with a seperate head and speaker cabinet. Fender used three different circuits in the bassman depending on the year it was made, they are the AA864, AA165 and AB165.

Specifications:
Control Panel: Black forward facing w/ white labels
Front Conrol Layout:Bass: In, In, Deep Sw, Vol, Treb, Bass - Normal: In, In, Bright Sw, Vol, Treb, Bass - Pilot Lamp
Rear Conrol Layout: AC Outlet, Ground Sw, Fuse (2A), Power Sw, Standby Sw, Speaker, Ex. Speaker
Knobs: Black skirted w/ chrome center, numbered 1 - 10
Head: 8" x 22¼" x 9" (20.3 x 56.5 x 22.9 cm)
Head Hardware: Black strap handle, 4½" chassis straps, corner protectors, cab hooks
Cabinet: 64-67: 21" x 32" x 11½" (53.3 x 81.3 x 29.2 cm) Late 67: 40" x 29½" x 11½" (101.6 x 74.9 x 29.2 cm)
Cab Hardware: 64-67: Black strap handle, 16" tilt-back legs, corner protectors, knurled studs, glides. Late 67: 3 black strap handles, corner protectors, knurled studs, casters
Head/Cab Covering: Black Tolex
Head/Cab Grille: Silver sparkle grille cloth
Logo: Grille mounted, raised, chrome & black, script "Fender" (head and cab)
Weight: Head: 30 lbs. (14.5 Kg) Cab: 52 lbs. (23.6 Kg)
Speakers/Load: 2 x 12"/4 ohms total (8 ohms each in parallel)
Speaker Model: Jensen C12N, Oxford 12T6 or Utah ceramic 12"
Effects: None
Output: 50 Watts
Preamp: Bass: 2 x 7025, Normal: 7025
Power: 2 x 6L6GC
Bias: Fixed Bias, adjustment pot (AA864) or balance pot (AB165)
Rectifier:
Phase Inverter: 12AT7 (long tailed)
Comments: Fender bassmans are well known for incredible guitar tones. They overdrive perfectly for rock and blues and original blackface bassmans command top dollar even in poor condition.