Tonequest article

jp said:

Guildmark said:

Help me understand "headroom" please. Is it the amount of volume you can get before the amp distorts?
Pardon me exposing my ignorance.

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That's the classic sound engineering definition, and I've always applied it to amps as well. However, I've heard it applied by some to define the raw power output of an amp as well.

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Same thing but a little different: "Dynamic Headroom refers to the ability of a receiver or amplifier to output power at a significantly higher level than normal for short periods to accommodate musical peaks or extreme sound effects in films.". Source John

As an example, the mike matthews dirt road special that I gave to my son, claims 25 watts, 65 watts "peak power".

Don't know what that really means, but it sure sounds good.

Peak Power: This is the maximum power that can be sustained by your audio equipment for a short period of time Source ... before catastrophic failure :shock: ? Another measure often recited in connection with power output / wattage; Frono mentioned this in another thread earlier, Root Mean Squared Defined ... need an aspirin?

Output for a a split second, I think and it sounds good from a marketing standpoint . When I first cracked it open, both of the 4700 mfd caps that they used from the output transistor to the speakers had failed. One was blown in half, so I'm guessing that whoever had it was exploring the limits of peak power.

Default said:

Output for a a split second, I think and it sounds good from a marketing standpoint . When I first cracked it open, both of the 4700 mfd caps that they used from the output transistor to the speakers had failed. One was blown in half, so I'm guessing that whoever had it was exploring the limits of peak power.

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" ... workin' on mysteries without any clues ...." Bob S.

I'm sure lots of musicians think of "headroom" in terms that go beyond the actual definition. Like me. I think of it as the ability to get clean (or relatively clean) sounds from an amp at higher volumes -- how loud you can get it to go before everything turns to mud.

The amplifier itself is only one part of the chain. Tubes and speaker choice (especially) play a big role. My GA40 would be quieter, more distorted at near max volume if it had the stock alnico speaker. With the Weber ceramic cali, it's both louder and cleaner at a given point on the volume dial. It's all relative ... this amp doesn't do clean as you'd hear from BF/SF Fenders. It's a matter of getting what clean there is to come through at a higher volume.

One of our BB Broz just sold a very fine-looking vintage Guild amp to this person: 'bahijadances'. We've been speculating (comiserating?) about the run-up in prices of the more better gooder vintage amps. Maybe we can ask 'bahijadances'; whoever they are, they are on a big-time buying spree having bought all the hardware listed below in the last 60-odd days :shock:

Gibson GA5 Skylark
Gibson Tweed GA19RVT
Gibson GA40 LP #1
Gibson GA40 LP #2
Tweed Fender Deluxe, $2,800

On another note: new Victoria GA40 - topic of this thread - sitting on eBay w/ $2,560 BIN Here Retail $$ unknown.

capnjuan said:

but I do hope the better boutiques stick around long enough so that their used amps come down in price ... maybe. CJ

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Well, you were being more prophetic than either of us realised...

I got a sweet, sweet deal on a 2005 Headstrong 5E7 (tweed 3X10 Bandmaster repro). Have only gigged it once yet, in a very bad sounding room, but it's a pretty awesome amp, especially considering I paid slightly less than what a used Fender RI Bassman typically goes for around these parts.

Meanwhile, my Weber tweed Super clone is blowing fuses already - it's going to my tech, and I'm going to ask him to replace every single component in the amp he deems inferior or not road-worthy. Very frustrating, because the way this little amp sounds and plays was growing on me fast.

Walter Broes said:

... Meanwhile, my Weber tweed Super clone is blowing fuses already - it's going to my tech, and I'm going to ask him to replace every single component in the amp he deems inferior or not road-worthy. Very frustrating, because the way this little amp sounds and plays was growing on me fast.

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:evil: Sorry to hear it Walter; nothing worse than an otherwise pleasing amp that won't stay on line. I know it isn't much comfort but blown fuses is probably an easier fix than squeal, fade out, and clicks/pops/sputtering. I'm sure your man can turn it around for you. J

Gibson Maestro GA45, 4 - 8" alnico Jensens $2,000 - closed eBay auction

Gibson GA20T - a poor man's +/- $1,500 GA40 Les Paul - auctioned off Here on eBay $475 or so ... maybe 1/2 of what it would have sold for in the first quarter of this year. If you compare the schematics, the GA20 has a 12AT7 in the channel one preamp instead of a 5879; both have 5879s in the channel two preamp. More likely than not it's the pentode 5879 - a power tube - in the preamp that contributes to the GA40's highly regarded tone. Otherwise, the only important distinction is the funky location of the GA40 volume control downstream of the phase inverter.

GA40 Les Paul http://www.schematicheaven.com/gibsonamps/ga40.pdf
GA20T Ranger http://www.schematicheaven.com/gibsonamps/ga20t.pdf



I took a bargain shot at it; still benefitting from some AAS abatement but am looking though for beater GA8; want to experiment some with the parallel 6V6s; just a crazy good amp.

Gibson GA20T - a poor man's +/- $1,500 GA40 Les Paul - auctioned off Here on eBay $475 or so ... maybe 1/2 of what it would have sold for in the first quarter of this year. If you compare the schematics, the GA20 has a 12AT7 in the channel one preamp instead of a 5879; both have 5879s in the channel two preamp. More likely than not it's the pentode 5879 - a power tube - in the preamp that contributes to the GA40's highly regarded tone. Otherwise, the only important distinction is the funky location of the GA40 volume control downstream of the phase inverter.

GA40 Les Paul http://www.schematicheaven.com/gibsonamps/ga40.pdf
GA20T Ranger http://www.schematicheaven.com/gibsonamps/ga20t.pdf



I took a bargain shot at it; still benefitting from some AAS abatement but am looking though for beater GA8; want to experiment some with the parallel 6V6s; just a crazy good amp.

mad dog said:

... The GA40 has a dark, hot sound, swirly and alive. West coast hot, jazzy too. Not much clean ... The amp itself is compression rich, so I can do without early alnico breakup. The clean you do get is so rich, dense, and the overdriven tone is not easy to describe. VG called it "chocolate thunder" ... funny but somehow appropriate.

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Based on Mad Dog's moving description of the tone of a GA40 and the relationship between the GA40 and GA20T Ranger circuits, I bought one (threaded here) , and then another, GA20T Ranger. I couldn't be happier with the first one but wanted one based more closely on the GA40's circuit ... and got one by dumpster diving on eBay. Some compare/contrast on the two circuits.

The preamp of the GA40 Les Paul is on the left, the GA20 on the right and, as a practical matter, the only difference is that the GA40 has a 5879 (green circle) in Channel 1 where the GA20 has a 12AY7 or a 6EU7 (probably later models; my other GA20T has a 6EU7 and a higher serial #). With minor exceptions, both amps have the same wiring for Channel 2 including an array of resistors and capacitors (red boxes) that cause a 'fluttery' or sort of foamy quality; similar to tremolo but without speed or depth controls and not as obvious. Both amps use a 6SQ7 as the tremolo oscillator (blue boxes) to make the volume go up and down and is controlled with speed/depth pots and a footswitch. Although not identified on the schematic, some/many/all? GA40s were fitted with 15" Jensens; the GA20Ts have 12" P12Rs.




The tubes used in these two amps are; the 12A_7 and functionally-equivalent 6EU7, the 6SQ7 - an odd-ball combination of a simple triode section on the left (1/2 of a 12A_7) and a dual diode in the other half (neither amp uses the dual-diode 1/2, its pins are left unconnected), and the 5879 on the lower left which has more in common with other output tubes like the EL84 on the right than it has with conventional preamp tubes like the 12A_7s.




So ............ ? It's the 5879s in both channels that sets the GA40 apart from its Gibson relations including the GA20T and all of ampdom back in the day and now. Since it's a single-section or single-stage tube, engineering departments might have frowned on its use; after all, twin-section 6EU7s/12AX7s did twice as much work in the same footprint/tube socket; why waste the space?

Why waste the space? Listen here:
Nocaster bridge pup through the Gibson GA40 amp (Channel 2: 5879)
http://www.ce.chalmers.se/~janjo/Vintag ... 40_Ch2.mp3
Nocaster bridge pup through the Gibson GA40 amp (Channel 1: 12AX7)*
http://www.ce.chalmers.se/~janjo/Vintag ... 40_Ch1.mp3
* This is a typo or a mistake; the GA40 has a 5879 in Channel 1, see above.

Vintage applications:
Kay model 720 amplifier
http://www.regiscoyne.com/kay720/
Vintage Ampex mic and preamps using the 5879
http://fixthatmix.com/ampex601ad_stuff/ampex601_ad.html

Current 5879 applications:
Snake River Amplifiers
http://www.treblebooster.com/snake_rive ... _works.htm
Divided by 13 Amplifiers; Model FTR 37
http://www.dividedby13.com/ftr37.html
Youtube: http://www.youtube.com/watch?v=YFlmMNnw ... 1&index=14
Abraxa Amplifiers; high end stereo
http://home.att.net/~abraxasaudio/proje ... t-pp1.html
Winfield Cyclone w/ EF86, similar to a 5879 in the preamp
http://www.winfieldamps.com/
http://www.radiomuseum.org/tubes/tube_5879.html

.... and the topic of this thread, the Victoria Electro King GA40;
http://www.svvintageamps.com/catalog/pr ... 5ec5f7d238


Gibson experimented with using a power tube as a gain stage and Victoria Amps, Divided by 13, and others have decided that's okay with them; it's ok with Mad Dog ... and it's ok with me too; a remarkable tube probably stepped over because of manufacturing economics ... and not because it lacked tone or didn't work well.

Versions of the GA40 LP; dates are approximate only.

GA40 Les Paul, 1952-1954 eBay auction and pics
3X6SJ7, 1X6SN7, a 6V6 pentode in the preamp, twin 6V6s/5V4 rectifier, 12" speaker.





GA40 Les Paul, 1955-1956 eBay auction and pics
twin 5879 pentodes, 1X7025, 6SQ7 tremolo oscillator, twin 6V6/5Y3, 12" speaker





GA40 Les Pau; 1957 - 1960
twin 5879 pentodes, 1X7025, 6SQ7 tremolo oscillator, twin 6V6/5Y3, 12" speaker





GA40 Les Paul; 1960 - 1962 eBay auction and pics
twin 5879 pentodes, 1X7025, 6SQ7 tremolo oscillator, twin 6V6/5Y3, 12" speaker
(this amp sold at auction with a 15", non-original speaker)

Rare Gibson GA90 on eBay In Italy, one of the several Gibson designs that use the 5879 in the front-end.

Gibson GA40 on eBay Last version ... auction includes interesting pics tying the model to George Harrison .... and a link to a recent closed eBay auction for same model but not in as good a condition ....

Beautiful Gibson GA45 Maestro on eBay Auction Link Cataloged and sold as an accordian amp ... see silk-screening on control panel. Preamp the same as the GA40LP; 5879s in both preamp channels, 6SQ7 trem, 7025/12AX7 PI; twin 6V6s, 5Y3 rectifier.

4X8" Jensen gold-frame alnico 5s. Possibly a re-cover; not just the freshness of the tolex but the speaker baffle doesn't look like the typical Gibson-standard cheesey 3/8" plywood and the retaining nuts on the speakers look like the speakers have been removed / replaced ... if not the originals they are model-correct.

Photo display and amp's condition helping push the auction price $1,925 with 16 bids / 8 hours remaining. Might get over the big 2 ... will be the most expensive Gibson to sell in an at-risk auction in the last year. J

John, I don't have a horse in this race, but to me the baffle, speaker mounting, and grillcloth (and tolex), all look original to me... compared to my GA-40 the baffle looks right for sure... anyway, doesn't matter but that's my thought on this amp. What makes you think those things have been replaced? It's in stunning condition. There's another one here, recovered, with an excellent video demo with guitar and harp:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0326282477

Hi Sean; maybe the flash washed it out but I guess I was looking for a more exaggerated grain pattern in the baffle board - auction pic left, my GA30 right. Would have expected it to be 'Gibson-standard' but doesn't have to be. In the auction pic, there isn't much visible grain suggesting MDO or a better-grade stained (birch?) plywood. If it had been changed, it would provide an explanation for the scarring on the speaker nuts ... although the scarring could be original too.

Not a requirement for the speakers to never come out but, given the vgc of the tolex and lack of baffle grain, if somebody had gone to that much trouble to shape up the amp, then the baffle might have been switched out too. I don't know what was original in the GA40s and GA45s but its little brothers all have the buzz-prone 3/8" plywood. Otherwise, the electronics are original to the bone. Followed the link ... these amps don't give a thing away! J

Bump: Sold $2,247 :shock: