Guitar Amps vs HiFi

[kt66se]

Hello,
Sorry, I have not posted on here for ages but I do drop by to see how things are going.
I am still the very proud owner of a KT88 and KEL84. I have to admit that I did swap out my KT88 for a Rotel 1582 power amp but it sounded worse so that amp is running a studio hifi in the attic.

I had a friends Marshall guitar amp to look at the other day that was faulty, one white top EL34, he agreed to swap out all 4 valves for matched pairs, rebiased and running sweet, then I had another Orange amp sent to me based on recommendation and that was a blown O/P transformer, replaced and now running well but.... I can't get my head round the amount of cheap components in these amps including the iron.

Why do we as hifi lovers spend so much money on high quality components when the music we are listening to is played through highly respected brand name amps using 1p signal capacitors and 10p regulation caps.

The musicians use the amps to record directly into their own studios and when on stage, use a mic to pick up the "Marshall" sound into a bigger stage amp which is all good I guess - I am just surprised at the cheap component count in these amps, the Marshall that I changed the valves out on cost the owner £800 - just for the head amp, was not a combo.

The Orange and Marshall amp uses fixed biasing and it would seem this is the common configuration for these amps - every time a valve is changed, or a new set put in, the bias needs setting and sometimes this is down to preference for the musician who may like the amp to run hot or cold. I set the bias to the EL34 datasheet based on the anode voltage and made sure there was no red plating but it looks to be a preference that could mean long / short life valves. (Why do guitarists call them tubes!)

Is this why these amps use fixed bias as opposed to auto bias as used in the WAD amps, I don't think WAD uses fixed bias?

I've seen EL34's, KT88's and a really weird Blackstar amp using a 12BH7A as an output valve all designed to be driven to the max - I have wondered what a guitar amp would sound like using high quality components and maybe one running in triode mode through some decent iron and a decent speaker - is there a philosophy / template for guitar amp manufactures to follow?

Sorry this is so long, just wondering aloud

[Richard]

Hello again Others will tell you more but I picked up a bit when our kids went through the usual electric guitar phase for a few years...

Hi-fi amps are just that; high fidelity, almost no distortion, just the amplification of the original signal to a level it will drive a speaker. Of course some do this better than others, and some listeners may like a bit of colouration added to their particular type of music, or tone controls to help a difficult room, so we still have listener preferences but they are small compared with guitar amps.

Guitar amps are part of the instrument and come in different types to suit a particular instrument or style of music. Apart perhaps from “acoustic” amps they only have to handle a narrow band of frequencies so the TXs wouldn’t usually be as wideband as hi-fi ones. Likewise the components will be chosen to suit the sound quality rather than accurate detail.

Lead guitar amps handle the usual guitar frequencies with various controls included or added to colour or distort the sound, and bass amps are designed for handling lower frequencies. Different makes also have their own sounds and we can appreciate the difference between a Fender “chime” and a Marshall “crunch” for example. Then there are lower distortion clean “acoustic” amps for, say, a voice input alongside an acoustic guitar input, which will reproduce a wide range sound with one maybe distorted a little and the other channel clean...

[kt66se]

Thanks Richard - totally agree on the sound front, wish they would put some decent components in though

Kind regards

Adam

[colin.hepburn]

Hi/Kt66/all
Yep back in my day with the Guitar Amps, the early Marshall amps did have good parts in them and were also point to point wired we did not use the Marshalls' no one liked them

we used the Hi-Watt Custom 100 amps instead also hard-wired tagboard construction. and very heavy I recently seen a restored one on eBay go for £2000 and going for more today we also used the orange amp's and the guitarist had his favorite Vox AC 30 EL84s
Here’s a link to that same custom 100 amp model we had

https://www.ebay.co.uk/itm/125281748...saAovXEALw_wcB

[Phil Y]

Hello kt66se

I think most of it has been covered but regarding fixed bias, I believe you can generally get a bit more power from a particular set of valves with fixed rather than cathode bias and that historically at least, was important. Also, as Richard said, the guitar amp is part of the instrument and so changing the design of the amp will change the sound. People buy a 100w Marshall because it sounds like a 100w Marshall. Changing the design would risk losing customers because it would no longer sound like a "Marshall".

Something to consider regarding cost is the cabinet work. Guitar amps are designed to survive years of use on the road being bounced about in the back of vans and trucks, thrown about by Roadies etc. They are built out of high quality plywood, all very securely jointed and glued and then covered in Tolex which in itself is quite pricey I believe. I don't know how much this costs but it must add significantly to the cost.

Phil

[kt66se]

Thanks - yes the enclosures all seem to be very well made. I have just been given a Fender Hot Rod Deluxe, this has got distortion and sending a signal through it, the bottom half of the sine wave is .... basically not a sine wave so I suspect something wrong at the phase splitter.

This amp has 2 5w ceramic resistors mounted right on the cct board and they are both touching each other, it looks like the tracking on the other side has scorched as well so there will be a bit of work checking this one out but why mount the power resistors so close to the board and right onto of each other - ho hum

I have a really old Sound City 100 in my garage which is a bit of a wreck, it looks like the Hi-watt shown on eBay, wonder if it's worth doing that up

Must admit though, I am loving working on these amps, so nice working with valves, with WAD kits, you build them, they work perfectly and sound amazing but that's it then - job done. It's great to see thermionic devices accessible and in demand because people love the sound of them

Thanks folks

Cheers

Adam

[Phil Y]

Hi Adam

One thing that might be worth a look, there is a guy on YouTube who does a lot of amp repairs including Fenders. He goes under the name of "psionic audio"
You might find some useful tips on modern Fender amps there.
https://m.youtube.com/watch?v=E3QLMz634lc&t=89s

Phil

[kt66se]

Hi Phil,
I found him this weekend while looking for anyone who had experience with distortion plus Stuart the UK guitar chap. Looking at Psionic it would seem like I need to change a lot of components to do a quality job, the phase splitter anode resistor had indeed gone open cct, replaced and now I have a perfect sine wave top and bottom but still got distortion so need to dive in a bit closer to find the cause of that (this is on the clean channel - tested to an external speaker as well)

Thanks again