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Topics - ilyaa

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1
Tubes and Hybrids / Mesa Triple Rec Woes
« on: March 16, 2020, 07:13:54 PM »
hey team!

trying to stay busy and keep working as the world burns....

and this stupid mesa triple rectifier is not helping my mood!

it has a weird hum (ground-esque) -

mostly on channels 2 and 3 but sliiight hum on channel 1, as well.

it stays, but quiet, if i pull V1 and goes away completely if i pull V2 -

its def in the preamp (half-split the amp, etc.) -

if i scope i see weird noise on pins 1, 7, 8, 6 of V3 that is totally not knob dependent - still there with knobs all the way down, and only the gain knob affects it. but if i cut out the previous part of the circuit, around V2, it goes away.

SO its clearly something around V2. i suspect some of the jfet/darlington muting stuff, but its gotten kind of hard to troubleshoot because i only have a dual rec schematic and it doesnt seem to match 100%.....

does anyone have a good triple rec schematic?

PS its not the preamp tubes i swapped em all and ive already replaced most of the Jfets and Darlingtons and smaller filter supply caps.....no change!



2
Tubes and Hybrids / Laney VC30 Output Transformer
« on: December 12, 2019, 01:06:25 AM »
if you were replacing a blown OT in this 30 Watt, 4xEl84 amp, which one would you get?

https://www.mojotone.com/amp-parts/Output-Transformers/Black-Brown-Vibrolux-Tremolux-Output-Transformer-4-8-OHM

or

http://www.triodeelectronics.com/22bastou.html

(not sure if they have that one - i e-mailed em)

or

https://www.mojotone.com/amp-parts/Output-Transformers/GA30RV-RVH-Output-Transformer

or

any other suggestions?

part of my issue is the stock transformer thats in the amp is very small - its snuggled between the second preamp 12ax7 and the PI - would like to find something small so i dont have to destroy the chassis putting the new one in.....

thank you!

3
Amplifier Discussion / Gallien Krueger 800RB
« on: July 22, 2019, 03:22:39 PM »
frustrating issues -

this amp has blown a few woofers - a pair of 10s in a 4x10 and a beefy EV 15 - it blew the 10s after about an hour and a half or so and blew the 15 in under a minute -

problem is, on the bench, it has no measurable issues. no DC on the output - shows me a perfect sine wave at full power on the scope - runs for as long as youd like with no visible problems.

im hesitant to plug it into an actual speaker because i dont wanna blow anything - any ideas what could be happening?

i asked the client about cabs and speaker wiring - the cabs and speaker cables were being used with other amps with no problems.

hmmmm....

4
Amplifier Discussion / Acoustic B-2 collaboration series schematic
« on: July 05, 2019, 09:05:04 PM »
Hey

Looking for a schematic for this amp

Particularly interested in the power amp - Zobel resistor blown, no way to tell what it was.

Thanks guys

5
Amplifier Discussion / Stramp hybrid schematics anyone?
« on: April 02, 2019, 01:01:40 PM »
hey!

recently came across a crazy old gem -

a Gun (United Sound Company) Lead 200

it looks just like this: http://www.vintagemusicshop.sk/?p=67295

with some researched i figured out its a later model Stramp - apparently, after he sold Stramp to Dynacord - because mine is a solid state preamp and tube power amp (with a tube PI). 100W 4xEl34 power section

has anyone ever seen a schematic for this hybrid?? its in rough shape and id love to get it going....

6
Amplifier Discussion / Polytone 102 Tremolo
« on: January 24, 2019, 02:02:30 PM »
finally got this amp almost back to life -

the power amp was busted and, because i could not find a schematic that seemed to match the amp i was looking at, i figured id just replace it with a simple class D thing. got a kit online and wired it up - it even fit the heatsink with no modifications necessary! - and the amp is working fine.

last step: the effects. the reverb is a bit weak (i think i can handle that), but the tremolo is not working at all. the good news is i found the right schematic! the bad news is, i really cant understand how the tremolo circuit is supposed to work - which obviously makes it hard to troubleshoot.

the right schematic is attached - can anyone with a bigger brain than mine explain how this tremolo is supposed to work? and whats that symbol by the LDR?


7
Amplifier Discussion / Simple SS Power Amp Build - +/- 40V Push/Pull
« on: December 04, 2018, 03:25:24 PM »
hey guys!

been a minute -

trying to clean out the crap pile while things are a bit slow at work -

i have this Polytone amp thats been taken apart for quite a bit now - the preamp is perfectly fine but somebody tried to "repair" the power amp and its just a total disaster.

the PT is fine and I decided I am just going to gut it and build a simple power amp from scratch so I can get this thing back to life -

I've got +/- 40V and heatsinks for two output transistors -

Also have a second, lower voltage tap (about +/- 20V) -

can you guys recommend a simple power amp build I can retrofit to this thing? its got a nice cab and a nice preamp with reverb and tremolo and everything - shame for it to die on this bench!

8
Amplifier Discussion / Peavey Musician Series-400
« on: March 02, 2018, 02:14:13 PM »
scratching my head a bit with this one -

got it in the shop with a transistor missing from the back (TO-3 sized hole on the chassis...) -

replaced that and replaced one shorted power transistor in the power amp -

with no load plugged in i get a good looking waveform on the output but once i plug in a load not so good - flattened out and clearly there's a problem -

some voltages are not quite as they should be - none of the transistors (power or driver or otherwise) in the power amp seem to be forward biased - even though they are all measuring fine diode-test wise - in and out of circuit -

the +/- rails are good, but the bases and emitters are all stuck at 0V or thereabouts - the symmetry of this amp is confusing me so i am having a hard time trying to isolate the problem without just shotgunning the whole thing -

any suggestions?

9
Amplifier Discussion / polytone 102 schematic
« on: December 26, 2017, 11:58:51 PM »
the amp I have does not jive with any of the schematics ive found online.

(http://el34world.com/charts/Schematics/files/polytone/Polytone_Schematics.htm)

someone has definitely dug around in here before. first warning sign was that both output transistors had been replaced with 2n3055. I know occasionally youll run across a power amp that uses two NPNs but this amp has +30 and -30 rails and none of the polytone designs I've seen resemble a dual NPN thing. there was also a shorted driver. but before I dig too deep id love to see a schematic...

this amp has the proper To-3 heatsinks for the power amp. it says Polytone 102 70W on the back. its a 1x12 combo. the power amp pcb has a pair of NPN/PNP drivers for each output. currently they are 2n3053 and 2n4037s. other differences from existing schematics:uurather than being .15 ohms, the resistors on the output are 15 ohms. and rather than being 100 ohms,uthe resistors on the bases of the output transistors are 2.2K

oh yeah and important detail: there is an 8 pin TO-5 old-style IC at the input of the power amp. unfortunately all the text has rubbed off of it....

I can post a pic soon - any thoughts in the meantimeu

10
Amplifier Discussion / ampeg ss140c heat sink
« on: November 26, 2017, 02:29:02 AM »
hey!

any thoughts for a suitable replacement heat sink for an ampeg ss140c?

got a salvage amp here and the heat sink is just *gone!*

someone must have removed it used it for.....something???

like the one in this pic: https://gbmedia.azureedge.net/usercontent/gear/3421921/p2_uhxjnxoft_ss.jpg?maxwidth=500

i doubt ill find that part - so im thinking maybe some of you guys have thoughts on what a good material would be to use/where to get something easy to fasten on there??



11
Tubes and Hybrids / fender bassbreaker 45
« on: September 13, 2017, 03:05:51 PM »
wondering if anyone has any documentation/schematics on this amp?

everything works and ive got a solid swing coming from the PI to the power tube grids -

but the output section is not happening - im getting normal plate voltage but ZERO screen voltage and -3VDC or so grid voltage - problem is this amp has a pretty complex thing going on with the variable output and mosfet control B+ (or whatever it is!) -

i know schematics are hard to find for these - anyone have thoughts on a similar circuit i could use for reference?

12
oh boy - everytime i have to pick this thing up im afraid its going to be the last time i pick anything up!

schematic can be downloaded here: https://elektrotanya.com/yamaha_pc4002_pc4002m_sch.pdf/download.html

anyway, here's a brief (i guess not that brief - buckle up) rundown:

1) belonged to a studio - sat around for a long time - inherited by another studio.
2) was going into thermal protection - i traced the issue to the left channel
3) took a look at the board - seemed from sitting around some solder connections looked cracked and not so good - did a general clean/resolder
4) went out of thermal - worked fine - i tested it running at 100 watts for thirty minutes or so - no problems
5) went back to the studio - worked for about 25 minutes then went back into thermal mode
6) got it back on the bench - once again issue in the left channel
7) this time, however, i noticed the fuse powering the left channel was blown
8) transistors measured okay - i plugged it in with a light bulb limiter and it worked fine - no thermal mode, but (because of the light bulb) the voltages were low so it wasnt quite in full operating mode
9) ran some signal through it - no problems
10) took the limiter off and plugged it in - worked fine for about 5 minutes at 10 watts then blew another fuse
11) check and got some bad measurements on output transistors - one PNP and two NPNs had blown
12) i took those out ran it without them and it worked fine at lowish wattage (10-25) for enough time to convince me it wasnt going to blow
13) OKAY i figured it was some bad outputs. ordered some new ones (these are hard to find dammit!), put them in, it worked fine for about 5 minutes then BLAM - blew a fuse and more outputs. these time they were different ones and in different locations.

any thoughts what might be going on here? i measured all the bias and load resistors they are fine - im particularly puzzled as to why its running perfectly fine for a few minutes and THEN blowing up - i dont wanna keep ordering these expensive resistors without a better game plan -

thoughts?

13
Amplifier Discussion / Sunn Coliseum 300 bass Schematic....
« on: March 19, 2017, 05:44:42 AM »
hey!

i know this probably is not a popular topic, as i just spent a bit too long looking for this schematic in vain.

wtf. i found one schematic for this amp and i was trying to work off of it for a bit until i started to notice some strange discrepancies - the IC used for compression in the schematic has 14 pins - the one im working on has 16! - the input IC on the schematic i was looking at was a dual op-amp - the one i'm working on is a 5534!

this is the schematic i was able to find: http://www.prowessamplifiers.com/schematics/sunn/Coliseum_300_Bass.html

anyone have one for the OTHER version, with the 16 pin compression IC and the single op-amp input IC? can't tell what the other differences are...

the power amp in working and im suspecting its the compression section that's the problem (seeing as the IC is fried beyond recognition) but i cant really work on it with this other schematic that doesn't match up at all....

interestingly enough i think this very amp has been asked about in forums through the years.......we'll see if i become just one of many!


14
Amplifier Discussion / yamaha CP30 repair
« on: February 08, 2017, 04:14:35 AM »
hey!

fixing up this old analog keyboard -

here's a link to the schematic: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwicodKMlIDSAhUH_4MKHfZIAzAQFgglMAE&url=http%3A%2F%2Fwww.bleeps-and-peeps.com%2Fimages%2Fstories%2Fhardware%2Fyamaha%2Fcp30%2Fservice_manual%2Fyamaha%2520cp30%2520servicemanual.pdf&usg=AFQjCNE9RQwQYVl8lBlOrCX86TcliSv4Zg&sig2=KwFP1a67oFJjWmA7ISqsdw&cad=rja

im not getting the -30V from the DC supply (see page 12). other voltages look fine - the AC coming into that section (the one that feeds TR7 and TR8) looks okay - about 30VAC - but im only getting 0.8V coming out of the bridge. thats my first suspect.

just a quick question: is there anything wrong with replacing this: http://www.sansui-vintage.com/product_info.php?products_id=98 with two 'discrete' diodes? say, 1N4007s?

15
Amplifier Discussion / MOSES mpx838 powered mixer output issue
« on: January 11, 2017, 03:13:57 PM »
hey everyone

working on this solid state powered mixer - main issue is i cant find a schematic anywhere so its a bit hard to troubleshoot it. its having a strange problem:

the output is nice and powerful, but once it gets to a certain volume, it starts to experience a periodic drop - every 1.5 seconds or so, the volume will dip between full power and 1/8 power - almost like a very slow tremolo. ive traced the problem to the power amp - it does not appear in the main preamp out, but does appear throughout the power amp. it only happens with a load plugged in - if i scope throughout the amp, all the way to the output transistors, when its unloaded, it works perfectly. but once a load is plugged in, the power amp seems unable to maintain full power.

now whats hard is that without a schematic i cant quite trace it properly - i was just wondering if anyone has a thought what might cause such a strange symptom?

its a long shot but anyone seen a schematic for this thing around??

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