Tube Bass amp circuits

[marcoloco961]

I have been wanting to build a Tube bass amp. A somewhat simple circuit so that I can experiment with some tweaking of bass amp circuits. I found this schematic of a tube amp that was supposedly a decent Bass circuit. I have to admit the wiring between the Tone stack and V4 output leaves me scratching my head a little. Anyone want to direct me to a link that will enlighten me on that section of the amp?

http://www.drtube.com/schematics/soundcity/sc100b.gif

Second, I couldn't find any real info on the trannys, but I found a couple of units I thought would work for this circuit online. (I am assuming the OT primary was in the 5K range from the tube specs, please correct me if I am wrong). Would either of these work in this circuit? There is a 4.2K or a 5K Edcor for the same price. Which , if either would work best in your opinion?

http://www.hammondmfg.com/1608.htm

http://www.edcorusa.com/Products/Browse ... eriesID=32

Also, would a 300mA HT on the PT be enough or should I go higher?

Thanks in advance for any help.

[VacuumVoodoo]

For a power amp, like the Soundcity, with 4xEL34 running at ca 410V you need an OT with Raa=~2k. A Hammond 1650T will be fine here.
V4 left triode has a Presence circuit wired as NFB link between anode and cathode, basically it's just a Baxandall active treble EQ with low turn-over frequency. Right triode is just a cathode follower feeding into the PI.

[roberto]

Check out this thread: http://ampgarage.com/forum/viewtopic.php?t=9568

I suggested a good sounding bass preamp, just try it.

[gldtp99]

It's interesting that you picked the Sound City L/B 100 Mk3 schematic as a basis for building a simple bass amp---i own two of these SC 100 watters and they are good sounding amps but there are much simpler (and good sounding for bass) circuits out there--the SC 100 Mk3 circuit is sort of a Hiwatt DR103 "cousin", without a Master Vol.
I also own a '72 Hiwatt DR103 and have built several Hiwatt clone amps from scratch---- the Hiwatt DR103 circuit is much better documented and works very well for bass duties.
For your project of building a simple bass head that can be tweaked to see how the changes effect the bass amp I'd suggest the Fender Bassman 100 circuit instead: http://www.el34world.com/charts/Schemat ... AN_100.pdf ---- Build the Bass channel only and you'll have a good sounding, simple bass head---- one preamp tube, one PI tube, and the 6L6GC x 4 output section. Also has a Master Vol.
I've serviced several of these Bassman 100's and the Bass channel sounds very good for bass --- the sheer simplicity of the circuit would easily show the tonal changes of any tweaks.
Magnetic Components has Fender replacement 100 watt transformer sets that sound great and are reasonably priced------ i've used several of their 100 watt OT's with 4/8/16 ohm output taps--- i've also used their 100 watt Fender PT's (450mA capacity) in different builds------ there's one in my mid-70's Orange OR80 clone I built.
If you're still set on the Sound City 100 Mk3 idea, i'd suggest the Hiwatt DR103 circuit instead--- loads of info here: http://hiwatt.org/ ......................gldtp99

[Bear]

there's one in my mid-70's Orange OR80 clone I built.

Have you tried those Orange circuits for bass? And do those need a Partridge or repro OT to bring out the sound, at least for guitar?

[gldtp99]

I've never run a bass thru my OR80 clone or my orig '74 Orange OR80------- i prefer bigger, cleaner tube amps for bass duties.
My '74 Orange doesn't have Partridge iron and sounds great (earlier Orange amps used Partridge)---- my OR80 clone has an Edcor OT (a 100 watter with 4.2k primary impedance) and it also sounds fine.............gldtp99

[KindaFuzzy]

The one I built is based on an ampeg portaflex. It's only 50 watts, but that's plenty for practice in the basement. Here's some pics: http://www.flickr.com/photos/35422385@N ... 218805058/

I attached a messy schematic as well. Nothing fancy, just standard input to a baxandall tone section with mid control into a long tailed pair P.I. and a pair of 6l6's. The mid control is really handy.

[marcoloco961]

Thanks for all the suggestions everyone. The DR103 looks interesting, just not having much luck finding info on a PT for it. The bassman100 looks easy enough and parts can be located fairly easily and at a reasonable price.

Quite a bit of difference in the specs for the two different (recommended Fender replacement PT) Magnetic components is a 420VDC @ 450mA, Hammond recommends a 640V @ 518mA. Anyone know the "proper" specs for the Bassman100 PT?

[Dr-Joned]

Marco,

If you are looking for info on the tranny for the 103 you can start here

http://hiwatt.org/tech.html

or check out the website here for total kits.

http://www.vintagehiwattrestorations.com/shop/

[gldtp99]

Thanks for all the suggestions everyone. The DR103 looks interesting, just not having much luck finding info on a PT for it. The bassman100 looks easy enough and parts can be located fairly easily and at a reasonable price.

Quite a bit of difference in the specs for the two different (recommended Fender replacement PT) Magnetic components is a 420VDC @ 450mA, Hammond recommends a 640V @ 518mA. Anyone know the "proper" specs for the Bassman100 PT?

The Hammond 290FX PT has a HT winding of 320-0-320V @ 518mA---see here: http://www.hammondmfg.com/pdf/EDB290FX.pdf
The Magnetic Components 40-18004 PT has a HT winding of 300-0-300V @ 450mA (giving 420VDC)---here:http://www.classictone.net/40-18004.pdf
Either PT will work fine for your bass amp project----the Hammond's specs make it seem to be a bit stouter----but i'm not sure if the specs are "loaded" or "unloaded"-----in real life use i'd suspect that the two PT's are close to each other and that it would be difficult to tell the difference----it takes @300mA to push a 100 watt output section to full power so either PT has plenty of extra capacity for the job.
Info on DR103 iron has been posted above---- the Heyboer Partridge clone Hiwatt replacement transformers are quality units---i've used several of them