Peavey AlphaB , what's the deal with ?

[catalin gramada]

Hello folks,
New trash yard discovery: alpha bass from Peavey, built in '90. They sold everywhere for 250-300 bucks around in working order. Something missing...As I did a little research it looks a very nice built sturdy 160W platform, and very serviceable. My honest opinion is built over mesa 180 and ampeg v4 which are three times more expensive as sh option. I allready ordered one expected to come, but is something I have to know about...? Why this ridiculous junk low prices please for what looks as a very well engineered designed equipment? You cannot buy even the transformers and tubes for price offer..Anyone experienced with please ?.Thanks

[Enzo]

It is the same old story, people look down on Peavey. And that is sad because they made great tough reliable equipment that worked as advertised.

[J M Fahey]

Musicians buy the magic potion, no interested into an actually working medicine.

Lots of interest on horrible stuff such as the Deacy amp only because "Brian May used it" or terrible Germanium based "Treble Boosters" and such and zero, or even worse, despise, for very well made and sounding Peavey and Crate stuff.

Because "Jimi/Jimmy/Ritchie didn´t use them" or equivalent, insert any Guitar God name there.

Only "respected" Peavey is 5150 ... you can easily guess why.

A Peavey Butcher is the IMPROVED version of JCM800 and runs rings around it, yet ......

Funny thing, if you compare many Ampeg and Crate amp schematics side by side, they have the exact same guts.

Not surprising since they were both designed and made by exact same designers, in the exact same Factory in St. Louis, USA.

But one of them has the *magic* Label

[tedmich]

people often hear with their eyes

[catalin gramada]

...well, I start to see why some peoples hate it...They tried to get some monopol using their own branded calibrated tubes. It is impossible to set the right curent for the tubes in this amp cause is not adjustable. This is a serious issue for any user. It is not impossible to modify a bit the power tube board to insert a 1 ohm resistor into cathodes and to replace a fixed resistor with a trimmer into bias circuit (I don't really like to use bias probes sockets adapters due to serious readings derive). Also something I dislike is the placement of elcos caps of bias circuit near close to power tube sockets, at least I have to make a board to place it into a convenient position....Power transformer looks small for 550w , that meant it will get very hot and need serious ventilation...will see...

[Helmholtz]

I don't really like to use bias probes sockets adapters due to serious readings derive...

Could you elaborate what you mean?

[catalin gramada]

Could you elaborate what you mean?

That mean residual contact resistance which could be significant using 1 ohm sockets probe adapters. I prefer to use 1% precision resistors soldered directly to the amp socket and leave it in place.

[Helmholtz]

That mean residual contact resistance which could be significant using 1 ohm sockets probe adapters. I prefer to use 1% precision resistors soldered directly to the amp socket and leave it in place.

Contact resistance is in series with the 1R sense resistor, so doesn't change the voltage across the resistor when connected to a current source (tube).
It is essential that the probe leads are directly connected to the ends of the resistor inside the adaptor.

That is a 4-point measuring arrangement and accuracy only depends on the precision of the resistor itself.

[Enzo]

I have to disagree, Peavey didn't sell specially graded tubes for the amp. Pretty much any 6L6 you want to use will be fine. The amp is designed cool enough that tubes won't be red plating. Just like they did on 5150 and other models.

There is not really room for a 1 ohm resistor for each tube, but there is a space by V10 where you could cut the trace and add a 1 ohm resistor for all six tubes.

Bias adjustment would be simple, make R9 variable.

This is a bass amp, so they expect no one will be trying to get the power tubes to break up, and so they bias it cool. And that is better for reliability and tube life.


As to the transformer, it has powered the amp for about 30 years so far, and hasn't melted.

And I agree with Helms, anay small resistances from the bias probe won't affect the readings, and surely will not affect operation while in use.

[g1]

They tried to get some monopol using their own branded calibrated tubes. It is impossible to set the right curent for the tubes in this amp cause is not adjustable.

I think you are thinking of Mesa Boogie. Like Enzo said, Peavey bias their amps cold enough to accept any tubes. They do not provide adjustment for the 'right' current as the right current is a very wide range.

[catalin gramada]

Why they placed elcos caps of bias circuit close near the power tube sockets? Isn't this the key to fail the circuit as fast as it can ? They choosed to place a very important circuit exactly in the most sensible termic area: between power tubes and hot power transformer, what the heck ...?

[glebert]

Personally I hate rackmount amps, even if there is a shell to mount it in. They are always more cumbersome than they need to be. I've had a couple of the rackmount Peavey tube power amps, thought about making a rig with a good preamp and in the end always would just prefer a regular head.

[catalin gramada]

No,no we can make it right. I just thinking...definitely the bias circuit will be pulled off and make it on separate small board exactly in opposite side (in dual bias adjustable version). Then will be enough room to run a bus ground return wire for power tubes along the edge in front of power board, isolate each power cathode by cutting original ground trace then conect from each cathode an 1 ohm resistor to the bus rail. Is a simple job which make the power stage more functional and safe.

Bonus: we may use 0.25- 0.4w cathode resistors to act as fuses just in case the bias circuit fail and the current rise to the sky.

I love this 80'amps as there are easy serviceable and prone to be moded...look how are designed newer generation of amps. I bet a lot of didn't worth the price to be serviced.

[catalin gramada]

I think you are thinking of Mesa Boogie. Like Enzo said, Peavey bias their amps cold enough to accept any tubes. They do not provide adjustment for the 'right' current as the right current is a very wide range.

well...

[glebert]

I don't think Peavey ever said "you need to use Peavey brand tubes." Fender sells tubes with their logo on them too.