About a Peavey Mace from the mid 70's

[Thomas P.]

After I did a cab job I really like to replace the transistors in the preamp because I think they're rather noisy. Most of the are marked SPS953 and 690. Would it be possible to use 2N5088 etc?

[Joep]

Hi Tomboy,

That can be tricky without knoing the original one.

Did you do a Google search on the original types? Often a piece of the component number is left out when it is stamped on a transistor. If you see 5088, you have to "add" 2N to make it 2N5088, or C1815 will be 2SC1815.

Goodluck,

Joep

[Thomas P.]

I did a google search but I didn't find a datasheet for it. The good thing is that I have the schematic of the amp and the preamps all look rather ordinary.

[petemoore]

Since you're inclined...seems you could just pull one, stick it in the Hfe of your DMM and figure out what's going on in that stage enough to pick some upgrade substitutions...
  Expecially if you have the schematic and you can discern the type; Bipolar, Jfet etc

[Joep]

What type of noise do you have buy the way?

Humming for example will (likely) not improve from new transistors.....Hiss is more likely to improve, especially if you use low-noise type like the 2N508x serie.

You can measure all the voltages on the E, C and B of the original transistor, to have some sort of reverence, before you replace the oldies.

Bye,

Joep

[Thomas P.]

Oh sure I know they're bipolar NPN and PNP.

It's more like hiss especially the reverb driver/return seem to produce a lot.

Here's a link for the schematic if anyone's interested:
http://www.peavey.com/support/searchmanuals/list/mace.cfm

[Paul Marossy]

I don't know why this is, but SS reverb/send circuits are very noisy compared to tubes, IME. It's OK at low levels, but when you turn it up... NOISE.  

[will]

Hi Tomboy,

I also have a Peavey Mace. I find it’s not all that noisy except in the presence of certain cell phones. However I find the SS preamp distortion sucks big time :x . It does sound really great loud and clean. I still have the 2 black widow speakers which are excellent.  

Oh sure I know they're bipolar NPN and PNP.

It's more like hiss especially the reverb driver/return seem to produce a lot.

Here's a link for the schematic if anyone's interested:
http://www.peavey.com/support/searchmanuals/list/mace.cfm

I took a look at the schematic regarding the reverb it looks like it’s using two 2N3904 transistors to drive the reverb. The 1st transistor is providing the gain the 2nd is an emitter follower to provide the current drive. The 1st transistor could be easily substituted with a low noise 2N5089. You could replace the 2nd transistor but since there is no voltage gain I would expect it wouldn’t contribute to the noise unless it was damaged.

I would normally expect the electrolytic power supply caps to be the cause of most of the noise. The electrolytic's usually have a 15 - 20 year life expectancy before they dry up and go bad.

I hope that helps.

Regards,
Will

[Thomas P.]

Will:
I thought so too. That's why I replaced all(!) electrolytics. Mines dated 1975 and all I've read at geofex the electrolytics go bad much sooner if the amp isn't used for a long time. And hey it sill got the original RCA tubes in it (maybe I should change them too sometime):wink:

I don't have the original speakers in there - someone must have replaced them :cry: But I came across a pair of celestions G12H from the early '70 :wink:

One of the biggest problems I have with it is the 'normal' channel which is very quiet and doesn't produce a clean sound. I believe the trannies are dammaged.
The 'effects' channel is very good and I really like its clean sound.

[will]

Hi Tomboy,

One of the biggest problems I have with it is the 'normal' channel which is very quiet and doesn't produce a clean sound. I believe the trannies are dammaged.
The 'effects' channel is very good and I really like its clean sound.

I find the sound to be exactly the same between the normal & the effects channel. Other than the effects channel had the extra mid tone control and the phaser. I must say I really like the way the 2 channels are set up on this amp. I have used the second channel for other guitarist, bass or for a mini PA, microphones work great in this amp.

I would just start replacing transistors in the normal channel till you find the problem. If you can maybe check the voltages, this might be really difficult, with the layout. I have never opened mine up as it works just fine.

I am only using 4 6L6 output tubes in mine and it is still the loudest map I have ever used. I think this was designed for stadiums. I'm wondering about just trying two output tubes. I would expect the amp to produce approx 50 to 60 watts, maybe I can get some output tube distortion when it is really cranked.

Good luck!

Regards,
Will