Peavey Classic 30 II 120US Tweed

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Bassman456
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Peavey Classic 30 II 120US Tweed

Post by Bassman456 » Fri Jan 15, 2021 1:49 pm

Purchased amp at pawn shop for grandson guitar player. There is a scratching high end sound that starts after the amp heats up. Scratching occurs on both clean and overdrive. Turning the treble control down muffles the scratching somewhat. Sounds like electrolytic cap in the tone stack having issues. BUT, I am seeing saw tooth wave forms on both HV and LV power supply circuits in the NEGATIVE side only. Of course there are multiple electro-caps paralleled for each supply. I also noticed that the clear LED pilot light is not working and it tests high ohm values in both directions when tested. Could it be related to the scratching and saw tooth I am seeing? All tubes check great on my testers. Tried to get a schematic on this amp so I can go thru it... but Peavey is very protective of their intellectual property. Amp made in China therefore so much for safety of intellectual property! :lol:
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Has anyone ran into these issues on this amplifier?
Does anyone have a schematic on this amp?
Can anyone offer some directions or recommendations for repairing of the scratching issue?
LED replacement is a no brain er.
Thank you, :D
Glen (Bassman456)

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Enzo
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Re: Peavey Classic 30 II 120US Tweed

Post by Enzo » Fri Jan 15, 2021 7:29 pm

Classic 30 as proprietary? Unusual, as Peavey is by far the most forthcoming with technical documents and support in the whole industry.


Sawtooth is ripple, and not scratchy sounding.

If I had to guess, my first suspects would be noisy plate resistors on a gain stage before the EQ.

Bassman456
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Re: Peavey Classic 30 II 120US Tweed

Post by Bassman456 » Mon Jan 18, 2021 5:50 am

Answer to "scratchy sound" after warm up. Found the problem and corrected. Small SMT cans 1uf/+50v electrolytic caps in the Send/Return circuit located between Treble pot and Send/Return Jacks on circuit board. Requires complete disassembly to get to these parts. C8 and C25 had cold solder joints, especially C8! Once amp heated up C8 acted up which is in the bypass area even though Send/Receive may not be used and it was charging & discharging creating the scratchy sound due to the cold solder joints! I replaced C8 and C25 while I had the board out due to the fact that you cannot get to these areas while PCB is mounted in place. They are tucked very deep under the face plate area, almost hidden.
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Burned out/Open LED D1 white/clear pilot light is located there as well. If the LED D1 pilot light was not working so I changed resistor R51 1.2k 1w to a 3.3k 1w and replace D1 Bright white/clear LED... reason is the DC voltage at R51 can run higher than 35vdc!
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I did the above changes and the amp works great now, no scratching and pilot light works at approximately 3.0vdc, 10ma. :D
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Note: While PCB is out, you may also want to check Q2, R22, R23 & R64 values! These are all hidden parts when PCB is mounted in the chassis.
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Just a extra note... In the DC power section for this circuit at 120VAC 60Hz regulated input power, the series R26 15ohm 1w resistor can allow the 35vdc to run higher! Other associated parts, regulated +/-15VDC power and tube heaters, etc., could fail if input power goes higher than 120VAC-60Hz. I backed my AC voltage input down to 115VAC-60Hz and in doing so I was able to measure 35VDC at R26. :o

Classic30inCincy
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Re: Peavey Classic 30 II 120US Tweed

Post by Classic30inCincy » Wed Jan 20, 2021 12:30 am

I'm glad you corrected your problem.

Classic 30 = 1st Class Amp !

PAF Classic Series Tube Kit.......Created By Classic30inCincy
Majic Mojo Tradename..........Created By Classic30inCincy
Graduate Of Joe Friday / Dragnet School Of Correspondence
Doctorate Degree Diplomacy From Royal Order Possum Lodge

Bassman456
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Re: Peavey Classic 30 II 120US Tweed

Post by Bassman456 » Sat Feb 06, 2021 8:07 am

Well, the Peavey Tweed Classic 30 II 120 has many issues! Tube sockets solder to PCB... bad news, over voltage occurs if your AC120 runs higher (121VAC-122VAC) the 36VDC voltage jumps up. Stupid idea to run 4 EL84 power tube heaters in series! Stupid idea to run 3 12AX7 heaters in DC and in series. DC heaters ok on 2 preamp tubes, but DC on the inverter 12AX7 driving the EL84's... who does this? Never seen Marshall or Fender do this. Usually AC heater voltage on Inverter tube.
The problem of scratching sound still exist after warm up. Treble control sort of mutes it some but it still sounds like a cat scratching. Now with a new JJ tubes preamps and el84's, the scratching still exist! I have changes all the caps for the inverter tube, correct the power resistors so amplifier sees proper B+ voltages and step downs, changed EL84 heater resistors to get proper voltage, bias on outputs tubes running at -14vdc as recommended. Grid resistors are equal at 1K 5W, bias resistors are all equal, re-soldered all tube socket connections at the pcb, re-soldered just about everything on the pcb.
Cannot test this stupid design out of the chassis! Cannot power up to check hidden parts covered by rolled over top flange... must remove circuit board and rely on test gear with NO power on the pcb! However... it is a heat up issue of scratchy sound after warm up. Can not do that with pcb out and on the bench. Caps and resistors check good and within tolerance on the bench.
PCB back in the chassis and all wire connections secured. Try again, same problem... touch o'scope probe to an EL84 input and sound stops, remove probe and sound comes back, do the same at the grids, same results. Output transformer working impedance can not be checked. Only winding ohm values can be checked with power off and transformer HV leads disconnected. Tap to ends (red to blue and red to brown) shows good ohm values but nothing to really check them against.
CHASING THE GHOST in this amp... using o'scope I find the noise thru-out the power tubes and inverter tube an backs up to treble control which controls the signal to the inverter for the entire EQ stack. Checked insulation by using SEND & RETURN jacks, cleaned both to make sure. Issue still present using loop cable. I am at the point of suspecting the output transformer HV winding breaking down after full warm up.
All testing above is with no input signal, all controls down to 0 except treble at half and clean volume at half. All switches out BUT switching states still have same issue in overdrive and boost positions!
The chassis on these amps have absolutely no place for the hot rising air to go, on venting on cabinet so all heat collects inside the chassis when mounted in the cabinet, yes another stupid design idea.
So chasing a bad ghost in this amp... its like working on a road weary HOT ROD that has inverted tubes and extended sockets to PCB and on venting!
Any ideas would be helpful other than trash it LOL, thanks.

Bassman456
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Re: Peavey Classic 30 II 120US Tweed SCRATCHING & OVERVOLTAGE

Post by Bassman456 » Sun Feb 28, 2021 8:19 am

Classic 30 II 120US Tweed scratching sound and power issues. In working on this amp I found a couple of issues that really blew me away. First of all the US 120Vac amp has a tendency to pass the power voltage difference from the primary 120VAC input power to the secondary side low voltage & High Voltage windings. Given that the basic resistors in the circuit are +/- 5% and +/- 10% problems can occur. Various US 120VAC power can tend to run at +/-3% voltage swing. If the input power runs low between 115VAC to 120VAC the amp is OK given the resistor tolerances. If the input power runs high between 120VAC to 123VAC... trouble starts to develop in numerous places. And to add to that the 4 EL84 power tube heaters are in series on the AC side of the bridge while the 3 12AX7 preamp tubes are on the DC side or the bridge. Note that series connected heaters tend to provide a sort of regulation for the low voltage circuits. Bummer if a tube heater opens allowing the voltage to run higher. Which can add to an already over voltage situation on the input power mentioned. So here's what I did to remedy the Scratchy noise & the over voltage situation.
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The SCRATCHY sound over layed on your guitar sound is the result of high voltage issues at some point in the SEND circuit. SMT PNP transistor Q2 is the culprit! You can replace the SMT Q2 and associated caps C8 & C25 as a fix. I chose to remove Q2, C8, C25, R22 & R64 leaving the R23 22.1K in place for impedance reasons. I then soldered a 1uf/100V Mylar cap the + side of where C25 used to be and the other leg to the + side of where C8 used to be. That stops the problem and still gives you a send output as well.
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LOW VOLTAGE DC POWER: Fixing the potential over voltage problems that can crop up on various unregulated 120VAC power input. I made the following changes to save several circuits in the amplifier. I replaced R37 & R38 with 410 ohm 5 watt resistors to save the EL84 heaters, I replaced R28 with a 30 ohm 5 watt to protect the 12AX7 tube heaters as well as the down stream circuits... especially the fixed bias! I had to replace the blown LED pilot light due to over voltage that had occurred plus I changed R51 to a 3.3K 2 watt resistor.
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HIGH VOLTAGE DC POWER: Again fixing the potential over voltage problems that can crop up on various unregulated 120VAC power input. I replaced R79 with a 410 ohm 5 watt power resistor, I replaced both R13 & R14 with 11k 1 watt resistors these changes help protect the screens and B+ voltages.
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After all of the above, I re-tubed the entire amp properly, powered up on my regulated 120VAC power supply and checked the voltages... all was well with no input, clean volume at 9 to 12 setting, treble at full 12 setting & all other controls at Zero, with amplifier speaker connected. Clean & voltages good after heat up and burn in for 1 hour... NO SCRATCHING, just your normal treble hiss out of the speaker. Shut off amp, moved 120VAC power cord to my household voltage the swings from 121VAC to 123VAC thanks to utility company. Turned amp back on properly, allowed heat up for 30 minutes, again NO SCRATCHING and checked all voltages again... all voltages were within 0 to 1 volt higher... GREAT! Shut down and moved back to regulated power supply set at 115VAC. Repeated test process above again NO SCRATCHING and voltage checks were within minus 1 volt.
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MORAL of this amplifier repairs... INVEST in a good solid, reliable 120VAC grounded power conditioner to maintain 120VAC at your amp. And NEVER run your gear on a GENERATOR without a 120VAC grounded power conditioner! Surge strips ONLY prevent over voltage spikes or surges typically above 130VAC and Joules rated. An always carry a 120VAC 3 prong wall outlet plug in tester that checks the wall socket for proper voltage, phasing & grounding BEFORE you plug your gear into that socket!

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Enzo
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Re: Peavey Classic 30 II 120US Tweed

Post by Enzo » Sun Feb 28, 2021 11:11 am

Trying to figure out where the over voltage problem might be. Every transformer ever made will raise the secondary voltages if the primary side voltages are raised, that is how transformers work. And if the primary goes up 3% so do the secondaries. Even the resulting DC will track. If you have 360v B+, and 120v mains, if your mains goes up 3v, then the B+ goes up 9v. And that is hardly a problem. And if your 36vDC heater supply goes up 3%, well that is about a volt distributed across the three, so 1/3 of a volt on each, not a problem.

The series heaters solve a problem that plagued many amps, high heater current. If we let the same current power all four power tubes then we only need current sufficient for one. Raise the voltage instead of current. It is current that burns out connectors, not voltage. Three 12AX7 heaters in series all run on the same 150ma of current. And if one opens, really that will have darn little effect on the power tube heaters. Besides with all those tubes dark, the amp won't have anything to amplify anyway. Those tubes run on DC heaters so there is no heater/cathode hum involved like there can be on conventional amps.

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Re: Peavey Classic 30 II 120US Tweed

Post by BriggTrim » Tue Sep 14, 2021 12:44 pm

Hi...Went to our nearby music store recently and the sales rep requested that I play a Classic 30 II. I disclosed to him I possessed a C 30 once and thought it sounded slender, weak and somewhat dormant! I went along with him and played through it,and shockingly it sounded pretty darn great ! Then, at that point I saw it had an alternate speaker in it other than that horrendous Blue Marvel ! It said Stevens something ! At any rate, is it another sort of speaker and did they do some other tweeks to it ?

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