AX84 BBS

Amp Parts and Kits

Doberman Music Products, LLC offers a variety of parts and kits

RE: Oscilloscope question(by Dave E)

Wed, 10 Mar 2010 21:31:47 -0500

I found this on ebay. It might not stay there very long since it's an old auction. Check out the last picture. It answers everything except what you asked. :) [link] I also found the manual. [link]

RE: Oscilloscope question(by Dave Nix)

Wed, 10 Mar 2010 21:20:01 -0500

you probably *cannot* test all the voltages in a tube amp without a set of x10 probes. I'd be wary of anything over 400v dc until you can verify otherwise.

First time P1 build, few questions(by Squidtubes)

Wed, 10 Mar 2010 21:14:03 -0500

Hello Friends! I have been reading from this site for a few years and finally decided to build a P1. I bought the components and made the board a few years ago, when the 060223 revision was current, so all of my build is based on that schem/layout. Here is a link to pictures of what i have so far : [link] On to the questions! 1.) Can I use a LED as a pilot light (resisted to 4.5 volts at 30 miliamps)? I don't really understand the 6.3v leads from the PT (269EX, the new one with 115 and 125 volt windings) , neither are marked any different, so is there really a positive or a negative? Current direction is of course a problem if not.. 2.) Could someone link me a picture of the input jack? I did lots of searches and couldn't find a picture of the jack like mine. It has three tabs, one for the ring, one for the tip, and one for the little grounding terminal that grounds the tip when no jack is plugged in. 3.) After reading the Paul Ruby startup guide, I am worried about a bleed resistor and was hoping someone had a good picture of this added to a P1 build. Anyway, I'd like to start with those questions, please feel free to look at my photobucket album there and tell me what you think :) I want to do this right, so I need to ax a few questions! Thanks guys

RE: The end of the Firefly PCB....(by Hankenstein)

Wed, 10 Mar 2010 21:11:31 -0500

John, do you have any kits left? If the Fly is gonna die, I need to get one as it's on my list. I just wish there was another method of payment than PayPal. Hank Schepers

RE: Completed my Hi Octane(by sjexperience)

Wed, 10 Mar 2010 21:09:44 -0500

hey spud, i'm with you on the recording stuff! i kinda completed my hi octane , yet i still gotta put some labels on the face plate and i hav to paint the cabinet black etc. I also sold my squier strat, so i am without a guitar now. Planning and saving for a Jackson DX10D which ofcourse i am going to modify with a switch for coil tap and get the single coil sound. Only thing is I am wondering whether i should replace the 3 way switch with a 5 way switch or with a push pull pot? ( considering ofcourse the push pull pot fits!!)

RE: Is U-TooB Great or What?(by joeyvoltage)

Wed, 10 Mar 2010 20:39:03 -0500

On 03/08/2010 @ 23:17, FredB wrote : : Armed with this, I'll be playing like Gary Hoey [link] in just a little while. : : Now if I could just get something that would slow down the vid so I can see what his fingers are doing while keep the same pitch... :) --

Simples, just take a look at the general position he is playing in, and that will narrow it down. dead serious!, although what works for him may not work for you position wise, so don't beat yourself up if you are not playing the same exact fingerings (some peple are really good at every inside outside picking combination, I have a hard time crossing stings using inside picking on the 4th beat when playing 4 note per beat groupings at a faster tempo.. around 140bpm or so). Also these nuances really do add to the character of the player.

RE: Loss of Volume on 50 Watt pp(by tgray)

Wed, 10 Mar 2010 20:25:06 -0500

Yes, of course that would be a good way of testing the connection.

RE: More 17x8x2 Available(by N Iversen)

Wed, 10 Mar 2010 20:23:10 -0500

hey brian, you got any of those chassis's left?

RE: LED for st-by(by tgray)

Wed, 10 Mar 2010 20:23:08 -0500

Merlin, You lost me on a few terms; antiparallel, does that mean a series connection? Also wattless drop, what is such a thing? tgray

Oscilloscope question(by Dan Moos)

Wed, 10 Mar 2010 21:31:47 -0500

I have a vintage heathkit IO-12 oscilloscope that seems to be working well. I don't have probes, and have so far just used wires with alligator clips. How do I know what the thing can handle? I have ordered a reprinted manual for it, but in perusing what is availiable to read online, I can't find this information in other heathkit 'scope manuals, and am not expecting this one to be any different. for instance, can I safely assume that I can test the full signal path of an amp? I know the currents are pretty low in a tube amp. This scope 'is all tube, and I would presume can safely handle the voltages in a tube amp since the scope itself is running on similar voltages. Any thoughts?

RE: Tube Alternatives(by MadDog)

Wed, 10 Mar 2010 19:45:34 -0500

...thanks, Ted. I tried soooo hard to forget that thing. Let's see, he's proud of never using a 12AX7. Anyone trying to get good tone is 'invited to die'. I'm thinking he's not exactly AX84 material.

RE: Diode Coring for Noise Reduction(by 3rdof3)

Wed, 10 Mar 2010 19:12:23 -0500

*10k resistor and 4th stage*

RE: Diode Coring for Noise Reduction(by 3rdof3)

Wed, 10 Mar 2010 19:11:34 -0500

HOLY BALLS! Total and complete silence when not playing ... I finally ended up using 2 IN4148's per leg between the TS and 10 resistor into the 4th stage. Also a .001 to gnd at the out side of the diodes. Kind of shocking at first. It does sound s bit like a noise gate at notes' final decay or when the Guitar's volume is turned down, but a step in the right direction nonetheless. Need to try those resistors. Might just hook it up to a switch on the front panel so one could switch between squelch-free signal or normal signal.

RE: L2L quirkiness(by IvanC)

Wed, 10 Mar 2010 18:47:19 -0500

Hey Brian. Well, I plugged in my amp, plugged the output into a 16 ohm 100W resistor and, connected a meter to each cathode (set to millivolts). I dimed the bias pot, dimed the MV and i've let it just sit there for about 15 - 20 minutes. My readings are: 13.1mV at V1 (R17) and, 13.9mV on V2 (R18). Using a 3rd DMM (Fluke 70), I measured my grids and they are: -39.3V on V1 and V2. The Cathodes initially took a few minutes to settle and then they (R17 and R18) were shifting around a little say, from 13.0 to 13.2 on one and 13.8 to 14.0 on the other. I then took Plate readings and they are: 371V on V1 and 362V on V2. I noticed my Cathode voltages would go way up (somewhere in the 80's) every time I placed the meter probes on the cathodes but, they would quickly go back down to almost the same values. They have now settled at about 13.9mV and 14.3mV. I turned the MV all the way down and measured the plates again and got 396V on each plate. So, if I understand you correctly, you're saying that you have roughly the same negative bias voltage (around -39V) on your grids and, about the same voltages on your cathodes, correct? If your plates are the same as mine, wouldn't that mean you're getting about 5W on each tube then, like me? 396V (Plate Voltage) * 13.2mA (Cathode Current) = 5.2W (V1 at 0MV) 371V (Plate Voltage) * 13.2mA (Cathode Current) = 4.9W (V1 at Max MV) As far as the bias pot, I got mine from Weber Speakers. It's a 50K Lin pot as advised on the schematic. I then plugged her in to my Marshall Wolverines (TSL 602 2x12 Combo) with the speaker selection set to 16 ohms and dimed everything except the MV. I have no squeal or nothing. When I dime the MV, I get plenty of hiss and a good amount of hum but, no squealing. With a guitar plugged in, it starts to squeal at less than 1/4 MV. Having said all that, you don't think it's worth changing R8? Maybe changing R27 to 10K as well? Theoretically, changing R8 to something like 220K will allow more bias voltage thereby, increasing output to 10W on each tube and, changing R27 should help with the NFB loop. Anyway, that's the latest. Let me know what you think. Ivan

RE: Got a Bogen, now what?(by Soundmasterg)

Wed, 10 Mar 2010 18:25:02 -0500

On 03/10/2010 @ 07:18, Zoe N Iain wrote : Hmm, all octal JTM-'80' with the 7868s for output? They need a little less driving than EL34s or KT66s, so the slightly lower gain of, say, 6SL7s in the preamp would get it back in the right ballpark in terms of the overall gain coming from each stage and the order they break up when pushed. Ought to be nice and fat sounding, too. There's nothing like an octal preamp for warmth and character ;-} : : Or an all octal JCM800, even. Never done that, but I can't see why you couldn't if you wanted to. --

I'm not sure that I want to get JCM 800 gain levels.....my current Vox AC100 build with a second high gain channel covers that territory pretty well so far I think. I was thinking more towards something good for jump blues tones. Something I could lug to the jams with a cabinet and solo away without being too gainy. I do like the octal angle...sounds like that at least would be a winner. Hmmmmm... greg

RE: Low power on a build, questions(by Soundmasterg)

Wed, 10 Mar 2010 18:21:56 -0500

On 03/10/2010 @ 07:33, steve25 wrote : Do you have a O-scope, is the output wave form clipping at 50 watts? : What is you total peak to peak A/C voltage swing across the PI outputs. You can measure this with out a scope, just your meter set for A/C. --

I do have a scope. I'll have to see if I can figure out the peak to peak output on the PI. I was at an engineer friend's house last night working with it and he was suggesting the PI was not driving the power tubes enough, but didn't have any time to troubleshoot further. Thanks for the help. Greg

RE: Silly Me...(by Mike Knauf)

Wed, 10 Mar 2010 18:14:37 -0500

The one I am referring to I bought from Doberman - whatever Chris charges for them, about $65 or so.

RE: Calling the experts(by S1vaD)

Wed, 10 Mar 2010 18:10:59 -0500

The amp is quieter with the new caps. The preamp tube doesn't flash when I turn on the heaters now. The cap inside the one I tore open was made by a Chinese company, best I can tell - Yageo. Extra lead had been soldered on a radial cap, and it was stuffed in a Rubycon wrapper. Looks like a 2002 date on it.

RE: Where Can I Get These Components?(by S1vaD)

Wed, 10 Mar 2010 17:50:37 -0500

I'm starting to get some cross talk. Houston, come in Huston. Burmuda? ...Come in, Burmuda! ...Houston, come in! What's going on... tracking station 43 Canberra, come in Canberra!... tracking station 63, can you hear me Madrid... can anybody hear me? Come in...! Come in...........! ULLAdubULLA and no American dates [link]

RE: Diode Coring for Noise Reduction(by Brian S)

Wed, 10 Mar 2010 17:20:20 -0500

On 03/10/2010 @ 17:00, 3rdof3 wrote : I tried it with 2M in parallel with 2 IN5408's and a .001 to gnd after. No big change. : : Could be the diodes or that I need to use multiples in the circuit as previously recommeded. Will pick up some 4148's today and give it another shot. : : The circuit is on my L2L between the 2nd stage coupling cap and G2 pot. --

I think that is where I tried it the first time also with dissapointing results. Put the circuit on a terminal strip and wire it between the tone stack and fourth gain stage or right after the MV like I did. Also, listen to the results before you bypass the diodes with the big resistor. I had a very large amount of hiss reduction until I put the resistor in. Went out during lunch and bought some 2.2m and 3.3m resistors as I think a larger resistor will work better. Will find out tonight. Brian

RE: Tone Stack Values(by stringbend)

Wed, 10 Mar 2010 17:07:39 -0500

On 03/10/2010 @ 12:42, RWood wrote : : This is a point-to-point (mess) wiring job so I am reluctant to rebuild the channel.

This I can understand. I only did one significant build using true PTP and instantly regreted it. It doesn't lend itself to the chronic obsessive complusive need to tweak the circuit the way tag board, et. al. does.

RE: LED instead of pilot lamp(by Ken Moon)

Wed, 10 Mar 2010 17:07:23 -0500

Here's where I got some nice white ones for a good price: [link]

RE: Behringer Ultrabass- how do you open it?(by stringbend)

Wed, 10 Mar 2010 17:03:50 -0500

On 03/10/2010 @ 14:25, Miles ONeal wrote : : Still hacks me off. I hate stuff that's *meant* to be disposable.

I've been using the same razor blade since 19... nah, just kidding. Perhaps it will help to think of it backwards (if you haven't already) and imagine how they installed it with such a short leash... they had the same constraint going in. It might suggest a cleaner solution.

RE: Tube Alternatives(by Peliass)

Wed, 10 Mar 2010 17:03:17 -0500

I thought I'd never see the moment when someone would finally mention the Metasonix F***ing F***er amplifier. Offensive is certainly what they are going for. Both in sight and sound.

RE: Diode Coring for Noise Reduction(by 3rdof3)

Wed, 10 Mar 2010 17:00:07 -0500

I tried it with 2M in parallel with 2 IN5408's and a .001 to gnd after. No big change. Could be the diodes or that I need to use multiples in the circuit as previously recommeded. Will pick up some 4148's today and give it another shot. The circuit is on my L2L between the 2nd stage coupling cap and G2 pot.