Need specs for the transformer from a Peavey Bandit 112

[Roflberry Pwncakes]

I'm trying to suss out the DC rail voltages in the power amp of a Bandit 112, so I need to know how much VAC is getting dropped across the bridge rectifier. I've got a parts list, but all it says is "X'FORMER I/P230V O/P", which is pretty vague... the shorthand in Peavey's parts lists is usually cryptic, but the actual component values are easy to read. The transformer has dual center tapped secondaries, but I don't think they're an equal pair because I've already worked out the voltage in the 2nd secondary that goes to the voltage dividers and zener regulators for the various transistor biasing and VCCs in the preamp, which is 16.7Vrms or 23.6Vp, and I know there's got to be more volts between the + and - rails than 47.2Vdc. The only thing I've got to go by is the voltage ratings of the 2 pairs of ripple smoothing filter capacitors set in parallel between the + and - rails and GND immediately after the bridge rectifier, and they're rated for 63V and placed between ether rail and GND, so I know there's less than 126Vdc between the two rails. I've Googled this already and the result was a mixed batch of reviews for Peavey's Transformer series of digital modeling amps and Hasbro's toy line. But hey, at least I know about the new $700 fully robotic Optimus Prime toy I'll never have. So in other words, I have searched high. I have searched low. But I cannot find anywhere that the VRMS value of the 1st secondary of that transformer is listed, but if anyone knows, it's one of you glorious basterds.

[J M Fahey]

PLEASE post the SCHEMATIC. Serious.
1 image=1000 words still applies.

In principle rail voltages are around +/- 40-42V DC so 30+30VAC , between 2A and 2.5A current or around 120-150VA

Itīs a very common value, so if you have an old transformer pulled from a similar amp, say Fender Performer, Randall RG80-100 , any Crate/Peavey/Laney/Marshall Valvestate rated 80-100-120W will be close enough.

Even a 28+28 to 30+30 VAC toroid from Apex Jr. who have one for about 23 bucks.

I am talking the main secondary, no clue about the second one you mention so again: Schematic!!!

[Roflberry Pwncakes]

PLEASE post the SCHEMATIC. Serious.
1 image=1000 words still applies.

Sorry it's low resolution, I tried uploading the entire service manual PDF but it was just a hair over what my max bandwidth is for my user level on here, so I had to take a screen grab.

[J M Fahey]

Thanks.
*Just* readable butbettervthan nothing.

Ok, besides the main winding I descrbed it also has an auxiliary one, about 18+18VAC to power preamp (it gets down regulated to +/-15V) PLUS it gets voltage doubled to get bout +50V raw which then gets Zenerd down to an unreadable value, so ina nutshell, you need an original spec transf0rmer, not abgenericone as I suggestd.

Are you only *calculating* values for some reason or actually need a replacemetb transfo0rmer?

If the latter, maybe you can get a dead/"for parts" Bandit for peanuts at a garage sale, Salvation Army, Craigslist, etc.

Why do you doubt the transformer?

[Roflberry Pwncakes]

gets Zenerd down to an unreadable value

It's +30v at the top of those 2 series zeners

Are you only *calculating* values for some reason or actually need a replacemetb transfo0rmer?

I owned a Bandit 112 once that blew up from thermal cascade in the TO-3 PNP transistor. It started pulling too much current and eventually burnt out a 1w resistor. While inspecting the board I noticed that another resistor tied to that node had already been reworked. The solder appeared less oxidized, and the color of the case didn't match all the other 1w resistors, and when I flipped the board over I saw that the technician had used a sharpie to mark the location. I contacted Peavey to order a matched pair of 73100AT TO-3 transistors so I could fix the root cause of what was obviously an ongoing issue. The person I talked to said that they didn't sell individual replacement parts, but they did sell full kits of every part placed on the PCB, but the price of the kit was nearly as much as the cost of what the amp retailed for.

I really liked that amp though, and out of all the amps I've owned it had the response that best suited my playing style. So I decided to put my 2.5 years of broadcast engineering education to good use and hand build a Bandit from the ground up with my own modifications to the preamp like a 3 band parametric EQ. I've already purchased a huge array of parts from Amazon and have already constructed the circuit that we discussed earlier that contains the zener regulated outputs as well as the voltage divider network on the preamp schematic that provides the biases and VCC voltages for the preamp transistors. I ordered an HVAC power transformer with a single 24vct secondary to function as a stand in to power the preamp so I can experiment with different transistors, troubleshoot noise, etc. until I can find a proper transformer.

If the latter, maybe you can get a dead/"for parts" Bandit for peanuts at a garage sale, Salvation Army, Craigslist, etc.

I'm always on the lookout for a vintage 1995 Bandit, but it doesn't help that I live in a remote rural area. It would be great to find a vintage Bandit transformer that's already got it's hysteresis burned in, or even a 'dead' amp that I could troubleshoot myself. The closest pawn shop is 30 miles away and their prices for used items are about 85% of new in box retail. I'm almost to the point where I'm seriously considering dumping the Bandit preamp into a tube power amp. It would certainly be a lot simpler, a tube power amp would require 1/10th of the components placed on a Bandit, and transformers for tube amps are pretty easy to come by. I went through 50 pages of transformers at Digikey trying to find something that I could use and there were at least 2 tube amp transformers listed on every page.

[J M Fahey]

Ok, but you did not tell me WHY do you want to replace that power transformer.

IS the low voltage winding working? YES/NO

[The Dude]

Juan,
The way I get it, he's building his own Bandit and needs a transformer for the build.

OP,
I may have missed it skim reading the thread, but it would help if you updated your profile location and/or tell us your mains voltage. It's hard to recommend anything without knowing this.

[Roflberry Pwncakes]

Ok, but you did not tell me WHY do you want to replace that power transformer.

I'm sorry, I thought it was clear that I'm attempting to DIY fabricate this amp from the ground up and need the transformer specs so I can shop for a match. I no longer posses the Bandit I burned out. After learning I couldn't order discrete components from Peavey to repair it (this was back in the day when online marketplaces like Amazon or Digikey hadn't been invented yet), it was just dead weight taking up space so I gave the Sheffield speaker to a friend and tossed the cabinet in the dumpster.

[Enzo]

Look up "Peavey semiconductor cross reference" and it tells you what all those transistors are. 70473100 are really Moto MJ15xxx series parts. Easily supplied from major parts houses. The only part in that power amp that is at all difficult to find is CR26. But you can find those in the parts market too.

I think Fahey touched on it, the transformer voltages don't matter that much. 42vDC rails might be average, but if they were 48v or 39v really won't affect the overall performance much. PV Bandit 112 export.pdf

The low voltage rails are zener controlled but the 25v rails from which they are derived are used in the power amp. But the transformer needed for those would be very common voltages, after all 15v rails are about as common as it gets.

[J M Fahey]

Ok.
Usual is people repairing and way too often worrying about the transformer, which in practice almost never is the problem, thatīs why I asked.

No, it was not clear you were building one , doubly so because most people try to build Tube, almost never SS.

With due respect, I would not attempt to build such a complex amp for starters (serious, I would not attempt to do it myself, after decades and thousands of amps made) , to begin with and this alone is a deal breaker: youīll go crazy trying to first design and then polish/tune the PCB

If anything, I would try my hand at an 80īs Bandit which still are killer amps but way more "doable"

Thereīs a reason MOST (as in 99% or higher) Home Builders choose Tube amps: circuits are WELL known, far simpler, no need for PCBs, point to point or eyelet/turret boards are more than enough, parts are robust so an error or accident burns a couple parts instead of nuking the full power amp, etc.

Besides that, the real crux for the home builder is the "metallurgical" part, specifically the chassis and front panel.

I suggest you but a dead or "for parts" Peavey Bandit (lots available) , and mod it towards the sound you are after.

What is specifically what is attracting you so hard towards THAT particular model?

.