Under rated Tone Beast Amplifier

Fixed Bias in the vc50 ( 5212 ) the vc30 Used cathode bias. Though i do belive from what i read they run the valves hard. And use they are known to chew through power valves.

Found a wee list of a few components to change to better qual items or a higher rated item as well as they are the most common failures in these amps.

So will change those, swap caps for nice new ones and relocate valves from board.

I'm shocked that they ran EL84s in fixed bias because, yeah, to get the tone that way running them hard witha hot bias is wise and if I recall it also requires more parts to set up an EL84 in fixed bias as the tube really lends itself to cathode biasing... now i wanna go abck and look at the pwoer section. Sounds like an oddball. I can only think they did it because EL84 production was really sketchy when that amp was released. I can only think of 2 current production amps that are worth mentioning that use fixed bais 84s, the jet city 20 watt and the Fender Blues Jr and the former was done for tone reasons while the altter was done for reliability reasons (and coes with a cold bias from teh factory to this day that really holds the amp back tonally). Upshot is that even run hard with tubes having a considerably lowr idle point instead of being at full or near full plate dissipation when the signal swings to the other pair you are going to drastically reduce the heat, so maybe you can use plan B. I still always worry about tube sockets arcing if a pentode fails though. Brian May's former amp tech, greg fryer, has this overengineered solution where every tube is indivdually fused. Pain in the ass to implement, but its kinda brilliant. Anyway, tube failure is the only reason to go abtshit and go with plan A now that I know its a fixed bias amp.... you know, ebing fixed bias I suspect its got a whole lot in common with the 80s hiwatt Lead 30. That's a single channel, but it has a high gain biacrown preamp that's clsoe to an 800 in conceptions tapled to a fixed bais 30 watt EL84 pwoer amp. They're very well regarded for non-highlight hiwatts. That explains a lot about this amp! I bet they amde the followup more of a high gain ac30 based on user demand and also beign able to source better quality 84s by the tiem they decided to create a new model... with low cost and affordable 84s you cna save a few cents on aprts going cathode bias.

I'm not surprised there are a few components being run close to their ratings, that's the crate curse... they were notorious for that on their early ampeg amps after aquiring the brand.

if you wanna get a bets of both worlds you could also cathode bias one pair and mimic the mesa 'simulclass' thing, a very cool trick in 4 power tube amps

Sure designer said he made it fixed for the immediacy and Leeding edge it gave to notes. Can only assume they used cathode bias in lower model 30 to reduce costs in the cheaper models. Same amp otherwise, same tubes, even same boars but with foxed bias components unpopulated and simpler cathode bias in its place

Valves run hard with voltage. 355-375 volts seems norm for them (bias seems to be 15.6v) and a few said run russian valves as they seem to handle it better. They came from crate with groove tubes (which at least at time i guess were also Russian). i may investigate the el84 heat sync covers that are supposed to drop bulb temps by 20deg and increase life a fair amount. Although it seems the fixed bias amp at least is a little cooler at idle than cathode ones

Obeid Khan was designer... He was asked what amp he'd play of crates and he said none. Apparently they challeneged him to design one he would play http://www.khanaudio.com/about/

Had planned to use Nos UK MOD valves as usually very well specced and built so handle being driven hard and are less susceptible to vibration. Have some Brimar cv4004 in my Groove Tubes Trio preamp and rather fond of them for same price as new valves (and how cheap they were compared to a lot of mullard ones).

Still need to plug the GT trio straight into power amp and see how it sounds. Clean channel is probably the best fender clean sound ever produced (black face twin and then some with some added magic). Crunch and Scream channels are no slouch either. Hopefully give me an idea how much of sound is from pre's and what power amp is adding.

the mil-spec russian 6BQ5 variant, forget the number, is a good bet for this amp... tubestore.com has been selling 80s nOS ones for ages, they seem to have an inexhaustable supply... the TAD 'STR' version of teh EL84 is simialr though soemwhat elss robust. Both of those 6BQ5 vriants have more of an RCA sound that's bordering on 6V6, and in fixed bais circuit you willt end tog et a more 'fender' response from the amp versus soemthing absed on Mullard or Telefunken EL84 specs. You would want to measure the space you have because the bottles are oversized on both of these EL84 variants.

I love the mil spec Mulalrds and Brimars from the 50s and 60s and use those and GE grey plates in most of my amps these days with the odd Russian tong sol RI or JJ thrown in.

Will hunt brimar MOD ones.

For interest. Here is designer playing from about 4.30 Not sure if one of his amps or maybe a jcm with his beat up Marshall cab https://m.youtube.com/watch?time_continue=269&v=hc3pjQSzdA8

sounds like an old 800, I used to have one, it has that grind plus upper mid honk accentuated by the cab... I could be wrong, but I don't think I am... tough to tell from a room recording with a camera microphone streamed via youtube though

He did design reason amps too And from what i read about him and amp design and tech work it's probs a home brew or highly customised.

another underrated tone beast? ampeg B25B (the non-B is kay too, basically the same except for an ungrounded power chord).... this is like a big portaflex circuit and works a treat for studio bass but is also a mean guitar amp. prices are still pretty low... not THAT low, you used to be able to buy them up at guitar shows for $100-200

He did design reason amps too And from what i read about him and amp design and tech work it's probs a home brew or highly customised.

I KNEW I knew his name from somewhere! Reason... they amde some nice cabinets too. The guy on the right just ash a superlead I think

another underrated tone beast? ampeg B25B (the non-B is kay too, basically the same except for an ungrounded power chord).... this is like a big portaflex circuit and works a treat for studio bass but is also a mean guitar amp. prices are still pretty low... not THAT low, you used to be able to buy them up at guitar shows for $100-200

Do like some of ampegs tones... A lot :)

my best friend still has my #1 VT40 from ym ampeg phase.... I gifted it over to him. Instant 70s stones machine.... and QOTSA if that's your bag. Loudest 40 watts ever. Sometimes I miss having ampegs, but I like the 70s ones and they're a maintenance nightmare and even worse for retubes! Its stilla rhd to find a decent 7199 pentode/triode phase inverter, you have to mod the amp for a 6AN8 or one fo thsoe otehr pentode/triodes. But the 7199 is so sweet, so so sweet.

New toy arrived..

Gibson Lab Series L7... ????

are they still cheap? I'm really partial to those Lab amps for jazz if I need more clean headroom then i can get from the normal channel of an ac30 (yes, I play jazz through an ac30 and yes they excell at it as logn as you don't need to be REALLY loud... my 1962 is one of the jazziest sounding amps ever because its a bass model so the lows extend quite a few hz lwoer than a normal model and the highs cna't get quite as shrill)...

my only complaint with the Lab amps is that Moog packed so many clever features in that theyt ake a while to set up, but man, great sounding amp, well voiced. Try a polytone some time too if you haven't (not sure how many you see in England, they're a USA jazz/session guitarist thing). they're still the same pricing they always were (CHEAP) I think and they're a great traditional solid state amp with a big, warm clean tone and very well thought out features. Up until the class D revolution I woulda said that the Lab amps, fender-lookin' Yamaha G series amps, roland jazz choruses and polytones were the onyl solid state guitar amps worth a damn. And all but the roland are bang for buck. I guess I should include that peavey stereo chorus dealie because it can out jazz chorus a jazz chorus, is more versatile overall etc but I left it off because its ludicrously heavy like up there with a marshall 50 watt 2x12 combo (at least the good 80s version I'm thinking of) and its so versatile with so many voicing features that it takes too long to dial in and is full of BAD sounds and just a handful of good ones.

So yeah, Lab amps, good call. If you want to play clean or you need a warm pedal platform and don't plan to use any effects that rely on pushing tubes to sound right then the lab amps are phenomenal... also, you can impersonate 70s BB king with one. I've never seen a Lab amp straight up broken either. iv'e seen them in need of service, but the amps are still working and sounding pretty decent... a few parts and they would be back to life and ready to gig. I'm not sure how difficult they are to work on though... PCB can be a bitch if its cramped inside. A lot of old Moog gear is well designed and serviceable but maybe not a ton of fun to work on and not for the inexperienced at all.

Mine was free but £100-150 depending on condition seems to be going rate. You see odd one listed high but it never moves. Like one on gumtree Southampton has one (l5) for £250 and that's reduced as has to go lol (and has sat on shelf in garage unused for 10yr)

Ye and look at price of a JC120. For me the optical compressor which is really high quality is much more useful to get a bit of varience in texture without getting too quiet (even clean it can be really nice to bring up those really quiet notes to hearable volume). Think i actually prefer the Lab Series (but been a while since played/heard a JC) and from what i hear so far some of od tones are much more useable.

Clean tone on lab is every bit as close as you can get to fender pre-gain control with bags more headroom and crazy clean volume.

O/D i am actually liking the Fender Quad cranked Freddie king sound for lead and again its a quality tone. Not so sure about some of other od sounds but led to belive it can be made to be very nice once your up on controls.

I imagine for warm Jazz the 1x15 (L9) may actually be Interesting, sure 2x12 Would be fine but really liking what the 4x10 produces a bit more presence, think a bit more avail clean volume too.

Iirc there was also the L11 which was a the 200w head (again real RMS) and would have huge headroom and volume + you can choose cab depending on size of gig or whatever.

Gonna enjoy this one though

Hopefully a link to some photos, 6 more in the album if click through :)

loving the circuit diagram on the back panel! never noticed that before. So Moog!

another bargain solid statey I forgot, the marshall lead 12 and 20 practice amps... they both sound pretty good for what they are, especially the 12! marhsall forgot how to make a solid state amp right after that though :-( they had it down in the early 80s