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It's old and full of tubes....TURN IT UP!

Riffraff

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Joined
Jun 16, 2002
Messages
165
A Plexi modded YBA-1 and a Les Paul......few things in life are more enjoyable than that. :biggrin:


Wait....mid century tube PA's a pretty fun too! '47 Masco MA25P, weird loctal preamp tubes, 2 x 6L6 power section and a big ol' 5U4 rectifier....nice Tweed Bassman vibe.


Les Pauls and old tube amps = bliss.
 
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jhmp

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Mar 24, 2011
Messages
717
Both sound great. Is that straight in, or any of those pedals utilized?
Traynor is a beast, the PA sounded much more modern than I expected. Nice tones!
 

renderit

Well-known member
Joined
Jan 19, 2009
Messages
10,401
I wanna hit that Masco with a P90 hard! Octal be so good. I thank Big Al for turning me onto them. It's what is in my At Mars Specialist Film-O-Sound. Liquid sex in a tube!
 

Riffraff

Member
Joined
Jun 16, 2002
Messages
165
The guitar is running straight into the amp in both cases. The amp is running to the Weber Mass 100 which is set to load. I'm running the line out signal from the attenuator through the DL8 delay and a Hall of Fame reverb pedals and then to the MosValve 1160 which is powering a ET65 loaded 212 (the pine box) and a V30 loaded 212 Carvin Legacy cab. It's a little trick I learned when I used to have a '93 Marshall 1959SLP that didn't have a MV or EFX loop. Running it like this let's you add your time based effects post distortion instead of running them in front of the amp and gives you complete volume control. It's really the same principal the Bad Cat Unleash, Power Station and other modern attenuator/re-amper units use. No dirt pedals of any kind are used in either clip.

I bought the YBA-1 several weeks ago. Except for a single biasing cap and a 1 ohm resistor on each power tube for measuring bias it was completely stock. I replaced the stock filter caps and did a little research and found what seem to be the typical mods which involve replacing the two volume pots and making a couple of resistor and cap changes in the preamp to nudge it closer to Plexi specs. I used pull pot on the bright channel that switches in a resistor and cap parallel to the cathode resistor of V1B so I have switchable stock and Plexi settings. It's a screamer.

Before

72%20YBA-1%20gut%20shot%20-%20small_zpscumwn9zd.jpg


After

YBA-1%20post%20mods_zpsa1miwspx.jpg



The Masco was a bargain Craigslist score.

That has "loctal" tubes in the preamp. Technically they are octal based tubes but a little different. Here's a pic of what they look like:

Locktals_zpstdtrtfrw.jpg


I got such a good deal on it I decided to send it to the Masco master Skip Simmons in CA for the conversion. He did a full recap, made a few value changes so channel 1 is dark and channel 2 is brighter with more gain then linked the channels 1 & 2. I generally set channel 2 at the volume I want then bring up channel one to fill in the bottom. It's basically the same principal you use when using the HIGH TREBLE and NORMAL channels in a 4-holer Marshall.

Before

MA25Pgut1_zps7e3ceab4.jpg


After

MA50015_zpse0b23d23.jpg
 
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sonar

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Joined
Jan 10, 2003
Messages
3,589
"Loctal."... I love it.

Yes, yes, yes... more octal love is needed in the amp world.
 

B Ingram

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Joined
Jan 3, 2016
Messages
730
... '47 Masco MA25P, weird loctal preamp tubes, 2 x 6L6 power section and a big ol' 5U4 rectifier. ...

If you'd like a frame of reference for those loctals (especially in price terms), the tubes are similar in performance to the below:

7B4: Essentially 1/2 of a 12AX7, but in the big-plate octal/loctal format. You could use the triode of an octal 6SQ7 if local availability dries up.
7F7: Equivalent to the octal 6SL7, which could be considered similar to the 9-pin 5751.
7N7: Equivalent to a 6SN7; obviously a LOT cheaper. 12BH7, 12AU7 and others are similar in a 9-pin format.
 

Riffraff

Member
Joined
Jun 16, 2002
Messages
165
The FIRST thing I did when I got that amp was grab a few NOS 7B4, 7F7 & 7N7 tubes. The good news is they aren't in short supply and are very inexpensive. I pulled those nice Sylvania 6L6GA's and tucked them away for safe keeping. They are REALLY nice sounding tubes that are glassy and round sounding with so much bloom it's crazy. I used pretty fair replacements in their place, RCA 6L6GC black plates. :teeth
 

B Ingram

Member
Joined
Jan 3, 2016
Messages
730
The FIRST thing I did when I got that amp was grab a few NOS 7B4, 7F7 & 7N7 tubes. The good news is they aren't in short supply and are very inexpensive. I pulled those nice Sylvania 6L6GA's and tucked them away for safe keeping. They are REALLY nice sounding tubes that are glassy and round sounding with so much bloom it's crazy. I used pretty fair replacements in their place, RCA 6L6GC black plates. :teeth

Nice!

As you saw, loctals usually are cheaper (by a lot). But some folks are getting wise to them and pushing the prices up. A hamfest is probably your best bet for getting them cheap. I made a point of noting alternatives because I saw AES was out of 7B4's.
 

Riffraff

Member
Joined
Jun 16, 2002
Messages
165
I'm a bit of a vintage tube nut too so I'm always watching for tube deals. I just pulled the trigger on one more Mullard and Amperex ECC83 tonight to add to my stash. ANOS tubes and strong pulls don't bother me a bit. :biggrin:
 
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