Tube Amp DIY'ers Club-DIY Bassman soundclips p.25!

[skunkyfunk]

ayos to sir ah!

may tanong lang ako sir. gusto ko bumili ng cheap solid state amp, kasi yun lang kaya ng budget ko. kung sakaling gusto ko sya ipaconvert ng tube amp, posible kaya yun??

eto yung amp. FENDER FRONTMAN 212R

Puwede iconvert sa tube amp yan, pero dapat:

1.  Papalitan ang chassis ng amp kasi mas mabigat ang components ng tube amp.
2.  Papalitan din ang mga transformer and chokes kasi mataas ang required voltage ng tube amps.
3.  Tatanggalin na ang PCB board.  Papalitan ng eyelet board yan para sa mga bagong capacitors, resistors, etc.
4.  Yung controls sa harap kailangan ng bagong design.

[BAMF]

Guys, drop in ko lang to...it seems to be a modified schematic for the Epiphone Valve Jr. Which again seems to be condensed from the P1 (which one ba came first ?) .

Great first tube amp project din to o... And Im sure, lots of great mods.

[Gibson78]

Quick question. For tube amps what are the ratings for the resistors? 1/2W? 1W?

Cheers and Beers!

[BAMF]

Eto pa something I leeched off. A vintage Kay amp. Also good for a first build :
 


Edit: uh-oh. This design is not safe, it takes its filament power directly from the AC mains. But for the brave....

saka....di kaya mahirap humanap ng power tube neto ? Hmm...

[BAMF]

Quick question. For tube amps what are the ratings for the resistors? 1/2W? 1W?

Cheers and Beers!

In my readings, the build notes always say "all resistors are 1/2 watt unless specified).

[BAMF]

Let's file this here na. Seems to be a good read :

http://www.instructables.com/id/Guitar-Tube-Amp/

[BAMF]

Another great first build project. A Fender Champ 5F1 !



Look ma! no tone controls !

[obelix]

ahhh.... the P1 iyan din ang balak kong gawin... ang mahal lang talaga kung diy... most of parts (turrets and board) I found sa rsphilippines din meron sila.

for the transformers meron duon sa wiredstate.

kaso ang mahal kapag isang bagsakan ang bili ng parts

[sd8450]

Quick question. For tube amps what are the ratings for the resistors? 1/2W? 1W?

Cheers and Beers!

The resistor resistance values and wattages are indicated by the designers of a specific amp. For amp DIY or restoration, one need to know and follow the required wattages shown in the schematic/layout of the specific amp one is working on.

It will not hurt though (for example) to replace a 1/2 watt resistor with a 1 watt resistor of the same resistance value. Substituting a lower wattage resistor than what is indicated may cause damage to the amp and could be dangerous.

Hope this helped!

[BAMF]

Hmmm...parang nabawasan ata posts ko dito ah. Must be a database backup restoration.

Anyway, most of the notes that I read on the tube amps say " all resistors are 1/2 watt unless specified" .

[sd8450]

Hmmm...parang nabawasan ata posts ko dito ah. Must be a database backup restoration.

Anyway, most of the notes that I read on the tube amps say " all resistors are 1/2 watt unless specified" .

It helps to simplify the schematic/layout. Mas numerous or most commonly used kasi sa vintage amps (like Fenders, etc) ang 1/2 watt sa preamp and tone circuits. May iilan lang na 1 watt sa power supply section at sa power amp section. Yun na lang ang kinakailangan i-specify ang watt ratings.

[BAMF]

Update : brought my P1 to the deltaslim clinic. After 2 hours, it gave out.

On the autopsy table, I found that all the tubes were good. It was the output transformer that opened, as well as one of the resistors in the power supply.

Apparently, in my attempt to make the amp hotter, I biased it to the maximum current that the tube can handle. The output transformer and the power supply resistor did not agree

So I rebiased for a more conservative output tube current and used another winding from the output tranny, one that wasnt blown out. It's working again.

Lesson: pay attention to the maximum bias current that the output tranny can handle as well

I got stinky, I got dirty, but sssseee...I learned

[paengkee]

holy crap this thing sounds awesome:

feature=related

P1 HO

[embot]

Hey BAMF Congrats on your first build!  Count me in as a member.

First thing, I don't think a hot bias will burn the OT.  It might destroy the output tube.  The Output tube may shorten out, then OT will go too. But that's unlikely.  In any case the output tube should have been destroyed too.  Chances are it's a speaker-output tube mismatch.  Double check the rating of your OT.  As a precaution add a 1K-1watt resistor to the output tubes screen (terminal 5 for octal tubes and terminal 9 for EL84s).  The resistor will burn before the OT burns.

About Output Transformers (OT).  Aside from the output tubes and the speakers the OT is the most significant tone generator in a vacuum tube amp circuit.  Just this weekend a bunch of friends and I were comparing two Epiphone Valve Jrs.  One was modified by adding high quality transformers and the other stock.  Both amps had exactly the same circuit and tubes.  We had both amps connected to an amp switcher so that we can change amps on the fly. 

To summarize the results, the modified one had better note definition in both clean and distorted settings. The modified amp also was more responsive and was actually a very nice amp.

I know that good OTs are expensive.  What I would suggest is for a bunch of guys buy a nice OT and have Mang JV clone it.

Good luck!

P.S.  That Mercury Magnetic transformer you have is a great OT for Dumble style amps too.  I've recently upgraded a Ceriatone amp with that OT and it made a huge difference.

[BAMF]

Ye ! Actually my P1, as of Friday night evolved into an HO, but wearing a hotter bias in the output tube. I added another 12ax7 stage.  I put the bias resistor to about 180 ohms to hit the 88mA bias limit for 6L6's...even if it was a 6550 that was in the socket. Ayun na nga, blew out one of the windings of the OT. I forgot...when I had that wound, I specified 5 Watts so mang JV calculated a maximum DC bias of 60mA @4k primary and 8 ohm secondary. I clearly blew the thing...I think the P1 amp, when biased hot can definitely spit out more than 5 watts and the 60mA handling capability of the OT. My bad. But the power tube was still intact after I performed the repairs on the OT and power supply resistor. But then again, medyo mura lang naman sya so I'll just use it again and when it blows, I'll have another one re-wound (hehehe). So far, it sounds very nice when you use it clean or dirty clean, but farts when you raise the gain knobs (its got 2 now). It's the crummy Rage amp 10" speaker. Kasi when I wired it to the 12 incher of my Fender Champ, ganda na ng distortion. Video soon when I work out how to use my webcam as a video camera .

Actually embot, I think the limitation here in the Philippines is that the winders here are using the silicon cores that are the same used for power trannies. I think may special wire pa for "bowteek" ones. So yun, given those limitations (for now), I guess we can enjoy tube amps up to a certain sound quality level. Tapos pag ready na, upgrade na to either OEM or Mercury Magnetics or Hammond.

Me screen resistor ang P1...its at 1k 1 watt nga ata according to the schematic...although I think i put in a 5 watter there hehehe. Like I said, my P1 was assembled from parts already lying around the shop...trannies I had wound but neglected, ditto with tube sockets and what not, so I just put together the motley collection of parts.

Before I get to continue the Spitfire, I'm re-doing my Fender Champ25SE to see if I can get a louder volume from it. I changed the OT already with a 40-watter, now the next step is to bias it hotter. Di pa yung Mercury Magnetics to, sayang naman, I'll save that for a Dumble clone or a Fender 5F6. Actually, di pa ko decided... pwede din Sovtek Mig50, dali lang pala yun. Soldano madali din, I just need to analyze it and cut out the unnecessary circuitry like for foot controlled channel switching. Maybe I'll even cut out the gain channel para the drive will come from pedals na lang. Pwedey !

[embot]

Undersized nga yung OT mo.  Even if biased properly, in a single ended design kaya parin magproduce nang 8 watts ang isang 6L6. Palitan mo yung PT nang mas maliit para malimit ang current to your output tube and transformer. Just make sure that the smaller PT can still supply the heater current nung 6L6 plus preamp tubes.

Incidentally, a higher bias will increase your amps headroom.  Lower the bias point kung gusto mo na mas mabilis ang dating nang distortion.

[BAMF]

Undersized nga yung OT mo.  Even if biased properly, in a single ended design kaya parin magproduce nang 8 watts ang isang 6L6. Palitan mo yung PT nang mas maliit para malimit ang current to your output tube and transformer. Just make sure that the smaller PT can still supply the heater current nung 6L6 plus preamp tubes.

Incidentally, a higher bias will increase your amps headroom.Lower the bias point kung gusto mo na mas mabilis ang dating nang distortion.

I think I get it, but just for confirmation...you mean bias voltage ano ? Kasi my experience is that the voltages can swing wildly, so I base na lang on the bias current as provided in the tube datasheets and calculate based on that. Tapos the higher the bias current, the lower the bias voltage so inversely proportional sila. So when you set the bias voltage lower, you're actually raising the bias curret and operating the tubes hot, that's why distortion comes very early, and when you raise the bias voltage you're lowering the bias current and operating the tubes cold kaya malaki ang headroom.  Tama ba gets ko ser ?

[embot]

Actually Jobet tama ka.  I take back what I said.  Sa Cathode Biased amp mas hot ang mabilis ang distortion.  I was thinking of a fixed biased amp sa reply ako.  Late na kagabi at di ko na alam ang mga pinagsasabi ko. 

[paengkee]

grabe sir bamf, you seem like you have a lot of money to spend on tubes and trannies if they blow out. haha

[BAMF]

grabe sir bamf, you seem like you have a lot of money to spend on tubes and trannies if they blow out. haha

Hmmm...not really. Some of them were collected over time. Like yung 6550's, I bought them maybe about 2 years ago, then they started collecting dust. I bought a Raon output tranny from Raon (it's not that expensive if it's local) then it collected dust again. Ditto with many 12AX7's that I used for my experimental tube pedals. They're not very expensive. Trannies from Mang JV aren't expensive either.

Ngayon lang sila nabuo-buo ba kumbaga .


Saka that's the thing. I'll never learn if I get scared of things that go "Boom". . Yung first airsoft gun ko, when I took it apart, I couldn't get it back together again. But I really learned (frustration learns you more than success ). Yun ang expensive...that thing was 12 thousand bucks. But after that, I became a gun tech and introduced techniques never before done such as polishing the guide rails, shortening the rails on the piston bodies and using Teflon lubricant. My AK47 goes up to 500+fps with "just" an M130 spring. Ooops OT na hahaha.

Pero yun yun. If fear stymies you, you won't learn. Be prepared for things that go Boom . Or things that make you go "OUCH !". Some call them failures, I call them "tuition fee"

[obelix]

hehe... wala bang pics?

[BAMF]

Okidoki. Here's the P1-HO. Obviously it used to be a solid-state Rage amp



Then the back shot showing the 6550 tube and 2X12AX7's :


Then for anyone interested, here's my Fender Champ with that OT mod, I slapped a 50-watt locally-made Output tranny. Ye, it did get louder just from that, but I'm still looking for ways to tweak it to the 50-watt level (hehehe kitams mo na ba sa wiredstate Q's ko obelix ?

[obelix]

Okidoki. Here's the P1-HO. Obviously it used to be a solid-state Rage amp
50-watt level (hehehe kitams mo na ba sa wiredstate Q's ko obelix ?

oo nga eh... daming marurunong duon.

balak ko rin gawing tube yung nag-iisa kong amp... wala pa lang money... medyo mahal.

[BAMF]

O guys, just came from Mang JV. The set of Trannies for my Matchless Spitfire clone only costs P700 (PP OT and PT na yun).

[obelix]

Huwat!!! great find iyan. point to point ba ang ginawa mo duon sa P1-HO amp mo?