Guitar to bass amp conversion

[4 Strings]

I just scanned through Gerald Weber's book "Tube amp talk for the guitarist and tech", and the "Tweaking your amp for bass" chapter got me started again.

Is there anyone who has actually performed a guitar-to-bass-amp-conversion?
Please tell me about it!

Which amp was the starting point?

Which changes were done to it?

How did it come out?

Are Gerald Weber's points valid? (I guess they are, he should know...)

The thing is that I need a relatively portable bass amp (combo, I guess) and buying a modern SS amp (Hartke, Ashdown, Crate - do they even make bass amps? - modern day Fenders and their yikes, sorry, their likes) doesn't appeal too much at all to me no matter how good they sound. I know, call me an idiot if you like. On the other hand, tweaking an old guitar amp appeals all the more to me .

[Tim Armstrong]

I haven't read that book, but I have gigged as a bassist with amps that worked equally well as guitar amps: SF Bassman, Traynor YBA-1 Bass Master, Crate PowerBlock, South West Electronics ss kit amp head with "fuzz" knob! (built by a friend).

As long as you run the amp into a bass speaker cab, you're good! I've never noticed a need for any circuit changes...

Cheers, Tim

[4 Strings]

Originally Posted by Tim Armstrong

I haven't read that book, but I have gigged as a bassist with amps that worked equally well as guitar amps: SF Bassman, Traynor YBA-1 Bass Master, Crate PowerBlock, South West Electronics ss kit amp head with "fuzz" knob! (built by a friend).

Cheers, Tim

Not to mention the Ampeg V4/V4B! Thanks Tim!
A V4B would be the dream amp for me (now look at that, there's a rhyme in there! Guess I better get myself some sleep now). Unfortunately the V4/V4B's seem to be out of reach because of their price. Besides it is a lot funnier rolling your own, innit?

I really like my SF Bassman 100 (for bass that is, I have yet to try it with my Partsquire). The SF Bassman 50 is a regal PITA for bass IMO. But my 100 has proved to be great, esp. with my Ampeg SVT 410-HLF cab. The only problem is that a SF Bassman 100 and the SVT make for a he££ of a load to haul around now that my car has died on me...

The amp I am thinking about converting to bass specs is a Traynor YGL3. I may be able to obtain a now-dead-but-easily-put-back-to-life YGL3 head at a reasonable price, and consider building it into a combo (how 'bout a 2x10 for example?). Someone told me that the YGL3 wasn't too far from a V4 sound wise, and if so, then all the better.

More opinions please!

[JohnnyCrash]

I'm about to convert a 5D8 tweed Twin (with a 35 watt OT) build into an Ampeg B15N...

[4 Strings]

BTW Tim, I just listened to those sound clips on your band's website. They sound great!

[4 Strings]

Originally Posted by JohnnyCrash

I'm about to convert a 5D8 tweed Twin (with a 35 watt OT) build into an Ampeg B15N...

NOW we're talking JC. Keep us informed as you go ahead!
Give us some details!!!

[Tim Armstrong]

Originally Posted by 4 Strings

BTW Tim, I just listened to those sound clips on your band's website. They sound great!

Thanks!

My '68 50-watt Bassman head sounded very sweet for bass, up to a point volumewise. The Traynor was better, I think, and I reckon a YGL-3 ought to be very nice (is that a 50-watt guitar amp, or a 100-watt guitar amp?).

Cheers, Tim

[4 Strings]

Originally Posted by Tim Armstrong

Thanks!

My '68 50-watt Bassman head sounded very sweet for bass, up to a point volumewise. The Traynor was better, I think, and I reckon a YGL-3 ought to be very nice (is that a 50-watt guitar amp, or a 100-watt guitar amp?).

Cheers, Tim

That sounds promising, Tim. This one, as I've been told, should be a 100 watts.

A.

[JohnnyCrash]

Originally Posted by 4 Strings

NOW we're talking JC. Keep us informed as you go ahead!
Give us some details!!!

It's gonna be a while - I have a lot on my plate :)

I've been using an AlNiCo 1x15" Jensen P15N for bass already, I might as well give it an old Ampeg to have a true old school bass rig!!

[4 Strings]

Bump!

I got a lot of interesting points from gentlemen Armstrong and Crash on my post, thanks guys! I believe there is no turning back now, guess I'll have to sell a sofa or two to get some room for yet another amp, so once again thank you very much...

How about you others, is there anyone who has tried any of the guitar-to-bass-amp-conversion mods mentioned in Gerald Weber's book? (Beefing up the power supply filter caps by a factor 2 or 3, tube to SS rectifier conversion, swapping out the output tubes for 7581A's, 7027A's, 6550's or others that work well with bass, larger coupling caps, about twice the capacitance on the tone caps and so on).

The last few days I have used my Tweed Deluxe (stock 5E3 specs) on a couple of occasions for some quiet bass playing while jamming with some friends. A low B+ stock 5E3 isn't exactly the perfect converter as described by Mr Weber, but I must admist that it sounds absolutely awesome as long as the volume is kept down. If I could find an amp that produced that same sound/tone at giggable volume levels I would do whatever it took to get my hands on one.

...as long as it incorporates a guitar to bass amp conversion and some solder sniffin' that is! So please share your experiences on this subject with me and our fellow TDPRI:ers!

[JohnnyCrash]

The only problem I see is in the iron.

Going to SS rectification, huge filtering caps, modding the preamp, and all of that is fine. Going to bigger power tubes may mean a current/draw deficiency in the PT as well as a possible impedance mismatch on the OT.

The OT may be a simple issue of doing some math, then figuring out what the new load on the secondary should be.

[4 Strings]

Originally Posted by JohnnyCrash

The only problem I see is in the iron.

Going to SS rectification, huge filtering caps, modding the preamp, and all of that is fine. Going to bigger power tubes may mean a current/draw deficiency in the PT as well as a possible impedance mismatch on the OT.

The OT may be a simple issue of doing some math, then figuring out what the new load on the secondary should be.

You're right JC! For the 6L6 to 6550 conversion Weber recommends leaving the PT heater wires connected to the 6550's and connecting the preamp tube filaments to an aux. heater transformer.

I recently tried to find me a 5V tranny for European 240 V primary voltage to use in a kind-of-5C5 build (the infamous Junkmaster mentioned in another TDPRI thread, now up and running, and great sounding too!). 120 to 5V trannies were plentiful, but I failed to find a 240V tranny for my rectifier so I had to make do with diodes and load the B+ down with a total of 188 ohms of sag resistors.

Which BTW leads me into another issue. How about using two 120-to-5V trannies to obtain 240-to-5v transformation? Is it possible to connect the primaries in series and the secondaries in parallel or vice versa? Never mind the extra cost of having to buy two trannies to do the work of one tranny. If I'd a-gotten into the DIY thing in order to save money compared to buying the stuff off of €-bay I would never have gotten into the DIY thing at all.

[4 Strings]

Originally Posted by JohnnyCrash

I'm about to convert a 5D8 tweed Twin (with a 35 watt OT) build into an Ampeg B15N...

JC, how has the 58D to B15N conversion proceeded?

[jefrs]

My WEM Dominator 25 Mk.II Bass is a 10W valve bass amp that has been modded to optimise it for guitar. It's a gain+master TMB. Essentially we fiddled with the tone stack and added a cap to the cathode of V2 to add more crunch. The other main feature is the speaker is seriously over rated, it's a 15-in 100 watt Rola-Celestion G15-100.

There's actually not much difference between olde stylee guitar and bass amps. Consider the Fender Bassman.

[Tim Armstrong]

If it's a tonal thing, we've been talking about the new-ish Hartke LH500 over in the bass forum. Apparently a BF Bassman (or possibly Showman)-style preamp feeding a 500 watt solid-state power amp. Get this: $350 at Sweetwater!

I want one VERY MUCH right now, but I just put $500 into car repair, so I reckon it's gonna have to wait...

Tim

[jefrs]

The OP 4strings wanted to convert an unspecified guitar amp into to a bass amp, not buy a new one.

So consider the schematics for the 6G6 /AA165 Fender Bassman. Look at the differences between the Normal and Bass Instrument tone stacks. The V2 in the 6G6 bass side has no cap on the cathode, this makes for a bit less crunch. My experiments with the WEM, which has a Fenderish tone stack and my Epi BC30, which seems to be based on the Bassman, make me think that the divider resistor between the treble and bass caps in the tone stack is crucial: a lower value gives more bass, more so than the capacitor values. The mid pot value is also important, generally they are too big and an A22k may be sufficient. One needs to maintain clear treble and mids but we need to get better control of the lower octave. The amp needs to be clean and crisp, it does not want all the crunch of a guitar amp although that is still there if the gain is cranked up. The speaker is not going to handle any more power than before but does need to cope with more excursion from big thumps and it wants more headroom. BTW that 15-in in my WEM is brighter than most 12-in speakers, you don't want a flabby speaker. And whilst most bass amps run to something like 300 watts, that's about clean headroom, my 10W WEM is just a small guitar amp but it can still shift furniture about with the bass through it.

So to convert a guitar amp to bass, all that may be necessary would be to change the speaker for one rated 10 times the amp, imo it does not have to be a special bass speaker. Incidentally, one method of breaking in guitar speaker is to play bass through them at fairly high volume.

[Tim Armstrong]

Originally Posted by jefrs

The OP 4strings wanted to convert an unspecified guitar amp into to a bass amp, not buy a new one.

Yep, and that was a year ago. I'm just offering options!

So to convert a guitar amp to bass, all that may be necessary would be to change the speaker for one rated 10 times the amp, imo it does not have to be a special bass speaker. Incidentally, one method of breaking in guitar speaker is to play bass through them at fairly high volume.

I've found it an excellent method of blowing guitar speakers! Twice!!!

Speakers designed to handle bass can handle the excursion required...



Tim

[jh45gun]

I would buy Eminence Speakers that say PA/Bass Use.

[4 Strings]

It's been well over a year since I started this thread, and yesterday I FINALLY got hold of the Traynor YGL3 trannies!

I only just lugged the iron home the other night, and all that I know so far is that they look OK. Quite dusty for sure, but not a single speck of rust on the laminates! The leads too look OK, not too short and with fresh looking insulation.

I believe I've tried to explain this question before, but I'll give it another try:

The YGL3 from which I ripped the trannies was a 90w guitar amp. What I'd like to do - although I am ready, able and willing to compromise all the way from here to the finished product in order to get the best result - is to use the YGL3 trannies to build myself a relatively low powered bass amp, i.e. slightly more than 50w but no more than 100w.

I also want the amp to be relatively simple, both circuit-wise and user-wise. That is I do not want a Master Vol and I'm thinking either a single tone control, a treble+bass setup or, at the most, TMB.

Most of all I want to make the amp old school sounding, i.e. fat, woody and woolly - reggae:ishly if you like - rather than modern sounding, trebly, tight and punchy.

Does any of this make sense to you?

So, whaddiya think, would a 2x6550 setup be too beefy (about 100w) for a bass amp using a 90w guitar amp OT?

What else do I want to consider?

BTW, I have not measured the PT's voltages yet. What could one expect to get off the HT's from a YGL3 PT?

I have built quite a few guitar amps, some with a few tweaks and stuff, but I have yet to design an amp from scratch and I have yet to build my first bass amp. So please bear with me here... I need any help and encouragement I can get, and I know that there is a lot of knowledge among you TDPRI:ers!

Thanks!