Music Electronics Forum http://music-electronics-forum.com/ This is a discussion forum about building , modifying and maintaing musical electronic devices such as guitar amps and effects. en Wed, 22 May 2013 16:48:14 GMT vBulletin 60 http://music-electronics-forum.com/images/misc/rss.png Music Electronics Forum http://music-electronics-forum.com/ Need good amp tech in DFW area http://music-electronics-forum.com/t33192/ Wed, 22 May 2013 03:59:43 GMT Can anyone recommend a good amp tech in the Dallas/Fort Worth area? I need someone who can troubleshoot/repair a humming problem on my Laney GH50. ... Can anyone recommend a good amp tech in the Dallas/Fort Worth area? I need someone who can troubleshoot/repair a humming problem on my Laney GH50.

Thank you. ]]> Thee Abomination http://music-electronics-forum.com/t33192/ US Masters TVA30 schematic anyone? http://music-electronics-forum.com/t33191/ Wed, 22 May 2013 03:50:02 GMT I've got one of these that walked in off the street with low volume. The usual external stuff (tubes, speaker) didn't produce any great change-my Princeton Reverb can kick sand in its face. This is a Chinese built import brought in by a firm in Wisconsin. I've emailed them for a schematic but no response.

It's a 30w head and cabinet, the head (so they say) is a fixed bias 4xEL84 setup with three 12AX7s and a channel switching setup with a gain channel. Sounds a lot like a Hot Rod Deville running EL84s. The reverb is very weak too.

I hope to heck this isn't another orphan.:thumbsdown:

I have a couple days

Does anyone know anything about this amp and the people who are selling them? Anything at all will be helpful before I pick up the phone and call them.

Thanks y'all. ]]> Prairie Dawg http://music-electronics-forum.com/t33191/ DR build humming http://music-electronics-forum.com/t33190/ Wed, 22 May 2013 02:07:48 GMT I just finished my 65 Deluxe Reverb build. Shook a couple of bugs out, but I do have two things I could use some insight on. First, it pops loudly... I just finished my 65 Deluxe Reverb build. Shook a couple of bugs out, but I do have two things I could use some insight on. First, it pops loudly when switched to standby. It's wired as the original AB763 schematic I believe, with the only difference I am using the filter supply board from the original re-issue. It is almost the same except in fact for the node on the hot side of the standby switch, (which as been discussed earlier in another thread) is using different value caps with an odd totem pole to simulate an electrically equivalent circuit. The re-issue didn't pop. Here is the re-issue schematic:

http://ampwares.com/schematics/65_Deluxe_Reverb_RI.pdf

The second thing is I have a hum, 60 or 120 Hz probably. I methodically pulled tubes one at a time until I am down to just the rectifier and 6V6s. I grounded B+, screen supply, and PI plates on one 18 gauge wire from the filter supply board to the star 1" from the PT, along with PT ct and line in ground wire. For the preamp plates supply I ran another 18 g wire to about the mid point on the chassis close to the reverb trafo. I have a beefy copper buss with the board grounds and control pots grounded at the end of the chassis next to the normal input. Outputs have 1 ohm resistors from cathode to chassis. No filament center tap, so 100 ohm resistors from each leg to chassis at pilot lamp. 18 g solid core, tightly twisted elevated pairs to each socket. What am I missing?

Oh, it doesn't pop with just the outputs installed.

http://www.turretboards.com/layouts_...verb_ab868.gif ]]> Build Your Amp Randall http://music-electronics-forum.com/t33190/ Marshall 6100 http://music-electronics-forum.com/t33189/ Wed, 22 May 2013 00:51:48 GMT I don't remember these being so crappy, looks like a Valvestate inside.
I think the later ones were changed a bit, but anyway...
I guess you have to unsolder the output tube wires to remove the output board?

Something intermittant in the fx loop, and that side of the board isn't properly supported and flexes like crazy so I'm sure there's some intermittant pc board connections. ]]> drewl http://music-electronics-forum.com/t33189/ Where Can I Post My Boast?? http://music-electronics-forum.com/t33188/ Tue, 21 May 2013 23:51:16 GMT After a full spool of purple plain enamel 42 awg wasted (as well as a few other parts), I finally wound my way to a pair of completed PAF style... After a full spool of purple plain enamel 42 awg wasted (as well as a few other parts), I finally wound my way to a pair of completed PAF style humbuckers for my SG Standard. The neck came in to a perfect 7.20k and bridge nailed a perfect 7.95k. Without having a gauss reading gadget yet, I went through a dozen or so bar mag combos including A2, 3, 4, & 5 - smooth and rough casts and gotta tell ya ... it was a major toss up between A2 & A4 but; the A2zz won!

Where can I post some dry, flat sound clips? I will demo through a Fender Hot Rod deVille 4x12 (60w), a 50W Marshall head & 2X12 Weber cab with his version of JBL D120zz, and, a 100w Marshall head with matching Greenback cabs. I will use my 2005 SG Standard for which these pups were intended.

I got bored with the 57zz I had in there and at my age, buying new pickups for any of my arsenal anymore would be just plain idiotic. Gotta thank you guys and this forum for gettin' me hooked on this winding/building thang!:thumbsup::thumbsup:
Where can I post these clips I'm gonna make? ]]> Beginner/ Hobbyist old guy http://music-electronics-forum.com/t33188/ <![CDATA[A question about the 'gimmick' capacitor on my SF champ]]> http://music-electronics-forum.com/t33187/ Tue, 21 May 2013 23:31:10 GMT (NOTE: since the 'gimmick' cap under discussion is not indicated on my schematic, I did not link a schematic.)

I've been looking over the CBS-era champ that I recently acquired, and one thing that I saw - that others have already talked about here on the boards - is the 330pF cap across the grid to cathode on the output 6V6. I understand that it is a roll-off filter cap to help avoid oscillations. While poking around the 6V6, I also noticed (The part that has me scratching my head):

There is a 'gimmick' of a few twists of the lead wire to the 6V6's grid with the HT wire for the preamp tubes. OK, so the small couple of pF capacitance (multiplied by mu, giving a slightly less small capacitance) will also act as to roll off high frequencies. Why did Fender include this when the cap across grid to cathode exists?

Does the reactance between the HT and the power tube grid add some kind of noise-cancelling effect? I'm thinking that if the B+ has a spike on it, then the capacitance will cause the grid to be tugged slightly in the same direction, and the effect on the plate tends to cancel out the excursion. Is there any merit to this? How far off base am I, and if there are discussions or resources that deal with this I'd love to see them (haven't dug anything up on it yet!). :):confused::) ]]> eschertron http://music-electronics-forum.com/t33187/ HiWatt G15 8 MaxWatt - Gone Silent, chip details needed http://music-electronics-forum.com/t33186/ Tue, 21 May 2013 22:32:42 GMT Hi, My HiWatt G15 has gone silent (much like someone else in a thread from 2012). Got the LED on so the transformer thermal fuse appears to be ok,... Hi,

My HiWatt G15 has gone silent (much like someone else in a thread from 2012). Got the LED on so the transformer thermal fuse appears to be ok, there is no his from the speaker, only a hum from the transformer and no sound from the head phone socket so pretty sure it's not a stuck headphone cut-off switch.

Looking at IC2 (the power amp chip on the heat sink) it's a bit tarnished near the legs and I think it's quite literally blow out. I've taken it apart but there is no identity on the chip.

Does anyone know what IC2 is and where I'm likely to source one (in the UK preferably). Is it a standard amp component or is this specific to HiWatt?

Cheers,
Craig. ]]> CosmicTen http://music-electronics-forum.com/t33186/ Humbucker mounting screw (holes) http://music-electronics-forum.com/t33185/ Tue, 21 May 2013 20:45:04 GMT As I understand it, a typical humbucker mounting screw is 3-48 (size 3 48 threads) ...but once I strayed away from fasteners based on a decimal... As I understand it, a typical humbucker mounting screw is 3-48 (size 3 48 threads) ...but once I strayed away from fasteners based on a decimal system (you Yanks are having a bit of laugh hanging onto imperial!) I started glazing over - can anyone link me to some nuts to fit pickup mounting screws? (cos a search on ebay for 3-48 nuts drew a blank!) ]]> Beginner/ Hobbyist peskywinnets http://music-electronics-forum.com/t33185/ Speaker magnetizer repair http://music-electronics-forum.com/t33184/ Tue, 21 May 2013 19:15:13 GMT A local speaker company has asked for help in getting their speaker magnetizer working again. It reportedly stopped working a couple of years ago... A local speaker company has asked for help in getting their speaker magnetizer working again. It reportedly stopped working a couple of years ago after a lightning storm, though that could simply be coincidence. It was custom built for them years ago, so all they have is this hand-drawn schematic.

Click image for larger version.  Name: Magnetizer.jpg  Views: 21  Size: 105.8 KB  ID: 23473

It's obviously a brute-force three-phase rectifier with a timing circuit.

For switching, it uses an octal plug-in relay inside the box to control the SCRs.

Based on what I can make out, the timing circuit's 20uF and 0.1uF capacitors are charged to a positive voltage when power is turned on to the unit via a large breaker box. Then, I'm guessing that when the switch (a big red momentary button on the front) is pushed, the discharge of the 0.1uF capacitor across the relay's coil is enough to trip it, at which point, the relay stays on until the 20uF capacitor discharges through the relay's 10k coil.

The other pole of the relay apparently switches to allow gate current to flow in the SCRs, turning them on. I've been told by a friend that the devices at the input are "Thyrectors," though I'd never heard of these before. He suggested that they were there to prevent spikes from getting fed back into the line.

If I help them fix it, I get free use of it for the foreseeable future. I'm thinking that my strategy should be to check the timing circuit first and them proceed to the heavier-duty components. The 20uF electrolytic capacitor in it looks pretty old, so it might have shorted.

Any advice/feedback is appreciated. With high-current power circuits like this, I understand how they work, but not necessarily the finer points of whether it's a good or a marginal design.
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]]> Music Electronics Rhodesplyr http://music-electronics-forum.com/t33184/ Cornford hurricane Blown Mains TX 2nd time http://music-electronics-forum.com/t33183/ Tue, 21 May 2013 18:57:10 GMT Hi All Ive posted a tread a week ago on this subject. Thought i would start a fresh one A quick recap Cornford Hurricane came in with blown... Hi All

Ive posted a tread a week ago on this subject. Thought i would start a fresh one

A quick recap Cornford Hurricane came in with blown mains tx. Got the original maker of the tx to make me one. Fitted it with a new set of Sovtek EL84 . Tad Bias meter
had them at 30ma each

Customer happy. He called me 12 hrs later tx blown again.

I got the amp back. 500ma mains fuse gone and tx burnt out. Spoken to the maker. he told me to send them both back. He checked them out. he didnt say they were faulty and it was the fault of his tx's ... But did replace it and send me an earlier cornford tx as well which is higher rated (Orginal cornford spec is 130ma for 295vac )

he told me to hook up that tx and run the amp flat out and monitor

I fitted a 160ma fuse and fitted the tx( Up rated tx ).Running flat out with a siginal gen on input and 4 ohm 100watt load on output
With the TAD Bias meter . Without siginal .. tubes are 30ma each at Flat out the tubes at 53ma and 57ma
volt meter set to ~ ma flat out 142ma (contacted though ac 295v ) with a guitar playing though it its about 120-130 ma

What im concerned about is that something it still drawing to much current. Im a little out of my comfort zone here.

Does anyone have any idea's or thoughts. Also im looking for some written info on testing the wattage of valve amps.


Blind boy benton ]]> blindboybenton http://music-electronics-forum.com/t33183/ Xicon 42TM018 transformer question http://music-electronics-forum.com/t33182/ Tue, 21 May 2013 17:54:07 GMT I'm building a pedal that is using the Xicon 42TM018 transformer. Looking at the space issues I'm having I'm wondering if I couldn't put the transformer on the other side of the board? This would mean the outer legs would be swapped on both the primary and secondary sides. Is that going to be a problem? The pedal is an A/B/Y box and the transformers are used for isolation. Is this going to cause any phase issues? ]]> Guitar Effects Bloodbath http://music-electronics-forum.com/t33182/ So they sent me E88CCs ? http://music-electronics-forum.com/t33181/ Tue, 21 May 2013 13:55:52 GMT Company I bought my 18 watt kit from sent me E88CCs for preamp tubes. Aren't these made for HIFI ? If any of you wise men would take a look at my post in Debugging maybe you could help me with some issues, give feedback on wiring , what I can do to make it better ?

Thanks a heap ! ]]> gtrplayr1976 http://music-electronics-forum.com/t33181/ Sessionette Power Amp Replacement http://music-electronics-forum.com/t33180/ Tue, 21 May 2013 12:43:58 GMT Does anyone know of an equivalent power amp module for the Sessionette 75 now that Award-Session are no longer supplying their SG75-PM120 unit? ... Does anyone know of an equivalent power amp module for the Sessionette 75 now
that Award-Session are no longer supplying their SG75-PM120 unit?

Thanks
Nick ]]> NickM62 http://music-electronics-forum.com/t33180/ Looking for a Egnater Rebel 20 schematic. http://music-electronics-forum.com/t33179/ Tue, 21 May 2013 11:29:24 GMT Looking for a Egnater Rebel 20 schematic.Thanks! Looking for a Egnater Rebel 20 schematic.Thanks! ]]> Schematic Requests overdrive2013 http://music-electronics-forum.com/t33179/ maybe this is stupid but how is it a signal and voltage travel together http://music-electronics-forum.com/t33178/ Tue, 21 May 2013 11:22:20 GMT What I mean is, you strum a note on a guitar, the signal travels through the circuit blah blah blah and then out of the speaker.At the same time a... What I mean is, you strum a note on a guitar, the signal travels through the circuit blah blah blah and then out of the speaker.At the same time a power source powers the speaker through the same connection. I'd like to understand how this works? Any input or suggested reading? ]]> Guitar Amps hesamadman http://music-electronics-forum.com/t33178/