Guitar to Bass amp conversion??

[Quilly]

Hi folks I'm looking at a bargain of a 50w valve guitar head that just needs an few EL34 power tubes. I'm toying with the idea of buying it for bass use. Is it possible to convert a 50W valve head for use with bass? is is a big job?

[pintspiller]

I would try it without modification first. It could be alright.

I had a MkII Superlead that my tech did a treblebleed bypass mod. It used a low input socket and I noticed the reduction in volume more than added bassiness to be honest.

I used my AOR30 and MkI Valvestate without modification with no issues before.

[No. 8 Wire]

On 04/12/2018 at 15:15, Quilly said:

Hi folks I'm looking at a bargain of a 50w valve guitar head that just needs an few EL34 power tubes. I'm toying with the idea of buying it for bass use. Is it possible to convert a 50W valve head for use with bass? is is a big job?

I don't know any technical details but there is no need to do anything to a guitar amp to run bass through it.  I run my bass through my h&k valve guitar amp with no problems, has a great DI tone! I don't use the guitar cab though for fear of damaging the driver.

Check this video, obviously clickbait, but some good info on the subject.

 

[Lfalex v1.1]

Random suggestion;

If it has an FX loop, input the signal straight into the FX return socket. That way, you'll bypass any guitar- biased EQ stages; effectively you'd be using it as a power amp.

It might deny you any preamp-related distortion, though, but a pre-amp pedal or multi fx might give you that instead.

Some amps I've used in this manner (both SS, mind) have given rather good results, and in both cases, the master volume has still worked, too.

[Bill Fitzmaurice]

Until roughly 1975 the only significant difference between guitar and bass valve amps was that guitar amps had reverb and tremolo, bass amps didn't.

[No. 8 Wire]

5 minutes ago, Bill Fitzmaurice said:

Until roughly 1975 the only significant difference between guitar and bass valve amps was that guitar amps had reverb and tremolo, bass amps didn't.

What changed after 1975? Always thought it was interesting that some of the most sought after amps are famous for both instruments. Hiwatts, Bassman, Super Bass for instance.

[danny-79]

Many many moons ago when I was just starting out on bass I had a 50w Marshall JCM 900 combo (we are going back to the 90’s) that I used to line out to a 15in PA bass bin. Could never get a usable volume out of it with out distortion. It was loud but no substance to it so soon got swallowed up in a band mix 

[Bill Fitzmaurice]

2 hours ago, No. 8 Wire said:

What changed after 1975?

That's when you started to see multi band EQs that were tailored more to either guitar or bass, and more emphasis on over-drive with guitar amps. Major differentiation was most common in SS amps.

[Quilly]

Hi Folks, Thanks for the info..I've decided to leave the head 'as-is' and simply get it serviced. Its a late 90's British made Carlsbro 'Top' 50W/25W head. I figured it was a decent enough guitar head and tinkering too much with it  it would ruin any potential re-sale value. I have a decent bass cabinet (Barefaced). I'll see what she sounds like after the service. I reckon if I keep the gain fairly low and drive the back end I'll be able to get a decent amount of bottom end. If I think its too 'guitary' I'll sell her to a guitarist that will appreciate it more.    

[Jono Bolton]

Not a valve amp, but I've used an old Sunn Concert Lead for bass before and it was great. For recording in the past I've split the signal through my Peavey Mark IV and an Orange guitar head to good effect.

[Sir Spence]

On some guitar amps, the coupling caps will be of a lower value and act as a high pass filter - swapping to a higher value (1000mf from memory) would give you the full frequency spectrum.

Assuming you want as little distortion as possible, running lower gain valves in the preamp will cut any preamp phase distortion down.

You might also bias the amp  right in the sweet spot to prevent any unnecessary clipping

 

..but this is all very much fine tuning - enjoy! 🙂

[Woodinblack]

31 minutes ago, Sir Spence said:

On some guitar amps, the coupling caps will be of a lower value and act as a high pass filter - swapping to a higher value (1000mf from memory) would give you the full frequency spectrum.

I think you might mean nF or µF  -  a 1000mF capacitor could give you quite a kick!

But if its just an input capacitor you want to change, knocking it up to double will half the frequency which will take it down an octave for bass.

And in general, I would just play through a guitar amp anyway (and generally do), the only thing you could fall foul of is that some guitar speakers dont have a long travel and can get a little heated with a lot of bass, but only when pushed a lot. 

 

[Beer of the Bass]

I'm not familiar with the 90s reissue of the 50 Top, but if it's the same circuit as the 70s version it looks like it should be fine for bass.  They had fairly low gain preamps, and the EQ was based on a passive James tone stack which usually works out well for bass use. 

[Quilly]

Here's a photo of one .(Mine is away being re-valved) .

I'll see what it sounds like with bass as-is. I have another 100W bass tube head so I don't really need another. Might be fun to have a 'dirty' sounding head for bass. 

Edited December 17, 2018 by Quilly

[Quilly]

On 15/12/2018 at 01:15, Woodinblack said:

I think you might mean nF or µF  -  a 1000mF capacitor could give you quite a kick!

But if its just an input capacitor you want to change, knocking it up to double will half the frequency which will take it down an octave for bass.

And in general, I would just play through a guitar amp anyway (and generally do), the only thing you could fall foul of is that some guitar speakers dont have a long travel and can get a little heated with a lot of bass, but only when pushed a lot. 

 

I intend to use a barefaced two10, so I should be OK. 

[Woodinblack]

58 minutes ago, Quilly said:

I intend to use a barefaced two10, so I should be OK. 

Yeh, there is no issue then.

[Quilly]

Really giddy at the prospects of firing it up. Taking an absolute age to get the valves sorted, 😫 I'm from the south coast of Ireland and my local shop has to send it to Dublin to a 3rd party...Still in the store a week after dropping it in !  😣 A Serious lack of amp techs here! 

[Sir Spence]

Quilly, what's the issue with the valves - are you trying to source specific NOS valves?

For current production stuff, I use Karltone. For NOS, there's a cabal of sellers around Billingshurst in West Sussex who you can find on Fleabay for are pretty reputable

[Quilly]

24 minutes ago, Sir Spence said:

Quilly, what's the issue with the valves - are you trying to source specific NOS valves?

For current production stuff, I use Karltone. For NOS, there's a cabal of sellers around Billingshurst in West Sussex who you can find on Fleabay for are pretty reputable

No - just a regular power valve replacement+bias and a general health check. It needs a once over anyway.