How A Valve Guitar Amp Works.

This is a great thread.

I built a poor AC30 clone in 1965 in my 2nd year at college can't remember what the output tubes were (807 power tubes) but they had 385v on the anode cap, for reasons that should be obvious I remember the voltage figure very well.

Speakers were a pair of 30w Etones which seemed to be the speaker of choice with the Oz amp manufacturers at the time, my 150w Lenard had 8 of them

I've been thinking of building a 5f3 clone or one of the 18 watt Marshall clones over on 18watt.com.

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Originally Posted by dave.king1

This is a great thread.

I built a poor AC30 clone in 1965 in my 2nd year at college can't remember what the output tubes were (808 maybe) but they had 385v on the anode cap, for reasons that should be obvious I remember the voltage figure very well.

Speakers were a pair of 30w Etones which seemed to be the speaker of choice with the Oz amp manufacturers at the time, my 150w Lenard had 8 of them

I've been thinking of building a 5f3 clone or one of the 18 watt Marshall clones over on 18watt.com.

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Cool, I'm not sure if I've ever heard of 808 Valves, let alone seen any, but I'm guessing that they were probably similar to the EL84 Valves, a good friend of mine, who's a Luthier, is in the process of having a 5F3 built for him by someone, the 5F3 is another one of those classic Fender amps.

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Originally Posted by DrNomis_44

Cool, I'm not sure if I've ever heard of 808 Valves, let alone seen any, but I'm guessing that they were probably similar to the EL84 Valves, a good friend of mine, who's a Luthier, is in the process of having a 5F3 built for him by someone, the 5F3 is another one of those classic Fender amps.

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Just googled and edited my post, the power tubes were 807 pictured, although there was such a beast as an 808

Attachment 13988

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Originally Posted by dave.king1

Just googled and edited my post, the power tubes were 807 pictured, although there was such a beast as an 808

Attachment 13988

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Geez, that's a pretty hefty Power Valve, I bet your AC30 build put out a decent amount of power and was pretty loud, how many of those 807's did you use to build your AC30?, that looks like a standard Radio-Transmitter Valve.

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Originally Posted by DrNomis_44

Geez, that's a pretty hefty Power Valve, I bet your AC30 build put out a decent amount of power and was pretty loud, how many of those 807's did you use to build your AC30?, that looks like a standard Radio-Transmitter Valve.

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It was a very basic single channel amp with simple tone controls and no effects 2x807 in PP, 30watts rms.

In 1965 it was a very loud amp but by about 68 and the birth of heavier rock it had nothing, hence the hike up to the Lenard 150W

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Originally Posted by dave.king1

It was a very basic single channel amp with simple tone controls and no effects 2x807 in PP, 30watts rms.

In 1965 it was a very loud amp but by about 68 and the birth of heavier rock it had nothing, hence the hike up to the Lenard 150W

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You probably could have been able to increase the output power by upping the HT and upgrading the output transformer, I think from the looks of it, you probably could have been able to easily get something like 100 Watts from out of two 807 Valves in Push-Pull, I've seen a single-ended Valve amp that uses a single 813 Valve and the HT was something like 1000V DC, or there abouts, but the amp was a high-end HiFi amp.

Okay, so how about we have a good look at a classic Valve Guitar amp from Fender, the Fender Champ, since it is a relatively simple design, it uses three Valves in the circuit, before I go any further I'll post a pic of the circuit for you:


Attachment 13999


Tomorrow, I'll see if I can post a write-up on how the Fender Champ circuit works, will try and make it fairly easy to understand, stay tuned.


Might also go into some history of the Fender Champ too.

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Originally Posted by DrNomis_44

...will try and make it fairly easy to understand, stay tuned.

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To quote our old friend Yoda...
Attachment 14000

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Originally Posted by Muzza

To quote our old friend Yoda...
Attachment 14000

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Cheers Muzza, some very wise words there, I shall re-phrase it to "I shall make it easy to understand".

Nice stuff doc, pity I don't have my Electronics 3 text book from 1st year at college I could have scanned the relevant bits.

It broke simple circuits such as that one into the various stages and explained how each worked how each of the stages interacted and how to calculate the component values for a given outcome.

I'm going to enjoy this thread because it will jog the memory, not only of the technology and associated maths but also some great times