Fender 5F1 Champ Schematic - Analysis and Breakdown

In this video I walk through the schematic for a 5F1 Tweed Champ guitar amplifier. I try to explain what the different components do in the circuit. I also discuss some different modifications you can make at each component to mod the amp more to your liking.
Time Stamps:
Circuit analysis - 2:28
Mods - 15:13
More videos like this here - • Guitar Circuit Analysis
Find some very cool merch here - / @kleydejong
Hit "Subscribe" for more videos!
kzbin.info_c...

[@pickrhead7185]

I'd strongly recommend Uncle Doug's instructional videos over this one. There are other good ones as well but Uncle Doug is usually about 95% correct in his understanding and his explanation & speaking is very clear. Beware, there's a ton of BS out there as well, not good when discussing tube circuits.

[@emmanuel-stone]

Thanks for taking the time to do this, it was really instructive :)

[@justinjayschneider5178]

great video Kley! thank you so much. will reference this many times as i build my first 5F1

[@rigosgarage5961]

This is an amazing walkthrough, thank you so much!

[@dennislemos7728]

nice video. I will definitely try some of your mods on my project. Thanks

[@bevfoster762]

This amp is ideal for first time modders. I have completed a clone & now doing extensive mods. your video very well presented. one very common error the input resistor tube 1 grid 1. Reducing the resistor to allow grid 1 be hit harder No effect - grid 1 is very high impedance, many meg ohms. The 1 Mr on grid 1 is to provide a drain for any stray electrons to 0V. The 33kr with the miller capacitance of V1 will reduce frequencies of 20khz and above. I am in the process of raising the gain of both 12ax7 tubes. Pots for bass cut, Baxendall treble - similar to 5f2a but not interactive with volume control. Raising the feedback from 2 db to 9.3 db (calculated). Presence & bass boost aka depth / resonance in the feedback loop. Raising the gain means larger value smoothing cap. 22 uF for V1, 100 uF for V2, 5 H choke (5E2) + 100uF+100r for surge limiter. Since gain increased - DC heaters 12ax7 is required . The effect of not having a bypass cap across V1 cathode resistor & feedback give a flat frequency response 50Hz , -1.4 db up to 20,000Hz +1.9 bd ,almost hifi

[@jarrodleerocks]

Great video. Very informative. I'm just getting into amp building and understand schematics as much as I understand Chinese. Thanks for posting

[@nicennice]

Great video. Think I am already hooked on this as a new hobby.

[@timwarneka]

Great job! Thanks very much for doing this video!

[@soundserviceelectronics2083]

A comment for the video creator. The 1M resistor when using the #1 input provides the grid return path for the input triode. When using the #2 input the 1M is shorted out and the grid return to ground becomes one of the 68K resistors with the other 68K resistor feeding the input in series. The grid is taken off at the mid point of the 2 x 68k resistor stack forming a 2:1 voltage divider causing a 6dB input signal level drop.

[@Blueguitar007]

If you plug instruments into both inputs at the same time does it take off the 6db drop? I read before that some bf sf Fenders do.. but I could be mistaken.

[@jimcatanzaro7808]

I only use 1 input at 33k if that helps anyone with a 1 Meg pot

[@T0mmyTune]

yes@@Blueguitar007

[@SMITHII_]

This could be confusing to a beginner, you say multiple times that "signal" is going into the tubes but you meant to say voltage. Specifically when talking about the rectifier. Also you forgot to mention that the coupling caps block the dc from the plate to grid and only allow the amplified ac signal from the guitar to pass through.

[@Roy-xe9is]

Perfect for beginners. Thank you!

[@DennisMurphey]

i just learned that an old signal tracer i have is built with 70% of the parts to build this Amp. Your video was educational and informative, I am looking forward to my project. And yes Modding the amp to see what happens. Should be a hoot and make a nice like practice Amp. Now i want to see what else you covered. D

[@AliKiani7887]

Very cool video, i really learn a lot of things, please make more videos .thanks

[@southerner66]

You cannot put a 1M master volume control in this circuit -- as you suggest might be possible -- because that would exceed the maximum grid resistance (500k in cathode bias) of the 6V6 as per the 6V6 datasheet. I'm one of those guys with 30 years of experience with this. Also, to date, all 5F1 Champs I've worked on, from various production years, had cathode bypass caps on the input stage from the factory, as did its virtually identical predecessor, the 5E1.

[@destaagengperwira]

So can i simply add a 500k pots for it? I have no prob with overall volume but my wife will.

[@joosboer1030]

I put 250k pot in that position and it works great

[@T0mmyTune]

it will. But what it won't do is what most would prefer it do, get the output tube up to full song. That, it will not do. What I do on mine is install an L-Pad attenuator. @@joosboer1030

[@caster168]

Good Video on Fender Champ circuits and MODS, I plan to mod my champ clone by adding a 20 MFD Filter with a 4 Hy 50 mA Choke, used by Fender 5Y3 circuits. FOR myself, additional videos modifications to this classic champ circuit. Again i enjoyed this video

[@caster168]

Also 1961-1963 Fender Tremolux 6G9-B It has Five 16MFD Filter Capacitors with a 4 50 Hy 50 mA Choke "GZ34"

[@pickrhead7185]

The 68k input resistors were put there mainly to prevent interactions between two instruments plugged in together - isolation IOW. Without them the instruments are in direct parallel & turning down one guitar's volume or tone would affect the other one's as well. That was the original thinking...also they provide a little protection in case the tube blows and sends high voltage to the grid and therefore the player (admittedly rare). The 1 megohm gridleak resistor stakes the grid reference to ground, otherwise the voltage will drift and eventually cutoff the tube's current flow altogether, called blocking. It's what sets the bias between grid & cathode. These resistors also help with oscillation & noise as mentioned.

[@SandersAmps]

Very nice break-down, and very practical. Thanks! Btw, everyone's a critic, but I found interesting snippets of practical application in your vid that I haven't seen elsewhere, so keep 'em coming!

[@brosephfreeman3144]

Great video thanks

[@kubockferre5532]

hi,id like to know what the secondary voltage of the power transformer and voltage on the 6v6 plate and voltage on the 12ax7 plate cause voltage is not there on this shematic thanks

[@MrSidecardog]

Aloha Kley, The 5F1 inputs are a bit more complicated than described. For single jack input, #1 is normal for a guitar. #2 is -6dB (25%) for dynamic microphones etc. However, there no level shift when both are used, they are both at normal level… the normally closed contacts on the jacks reconfigure the input resistance to make that happen.

[@MoggioMTB]

Well explained!

[@destaagengperwira]

My first 24 minutes without stop youtube vid. Thanks and congrats for this knowledge. Maybe one or two mistake (or non mistake) but it is very useful for me. May i email you for a question or two?

[@bassblom]

super cool video, thnx! I am going to build me a 5f2 with mercury magnetics irons.. in a recent trade I got me a JBL K120 alnico 8 ohm.. how will that end up? it might get loud? :D

[@AllanBelt]

excellent, one question: i hava a fender champ that distorts bad when put a feedback resistor (22k)and it´s cleaner when i disconnect it.

[@JohanSegeborn]

Thanks! Great video

[@KleyDeJong]

You're very welcome! Any thoughts on other amp circuits for future videos?

[@mrbigg7255]

Knowing Johan, Marshall Plexi would be his choice😂. Check his channel out.

[@jameswallace5967]

Really good video. Perhaps you could look at the Vox ac30 JMI years...

[@andrefiset3569]

I build 2 5f1 clone at this point and i am curious about the power transformer output, Online calculation ask for a 50 mA and the hammond remplacement 100 mA. 50 mA is enough?

[@MaraPhelps]

THANK YOU!!!

[@MrSidecardog]

Aloha Kley Moving master volume to the 6V6 grid will cause coincidental bias variation on the output tube. Self leak grid bias should not be variable once set.

[@christophervillanti1417]

The 5Y3GT is spec'd for a 10mf capacitor as the first input capacitor. I would increase the second one in the chain rather than the first. The 16mf is already pushing it and going higher will shorten the life of the tube. Very well done overall.

[@caster168]

The 5Y3 data sheet does spec'd 10 uf 450v electrolytic capacitor and a 10 henry 35mA transformer filter choke. There are schematics with the 16 uf electrolytic with a 4 henry 50 mA transformer filter choke. For myself, i plan to build a 5y3 with FOUR 16 uf 450 volts electrolytic with a 4 henry 50ma transformer filter choke. For a clone build, it's worth building.

[@caster168]

Uncle Doug video on Champ like circuits are Negative Feedback Loop Pot, a transformer filter choke, and a OneK 6V6 grid resister.

[@caster168]

D-LAB STEPED UP the filter capacitor in series 33 uf, 22uf, and 10 uf 450 volts

[@caster168]

Thanks Chris, i learned a lot from your post, and thanks Kley for this video

[@caster168]

Finally, RobRobinette website cites Increasing the value of the first power supply filter capacitor or adding a choke can reduce voltage sag and stiffen the power supply. They can also firm up the bottom end because it takes more power to amplify low frequencies. Keep in mind tube rectifiers have a first filter cap size limit so reference your tube rectifier's datasheet to keep from overtaxing the tube at turn-on.

[@marcojp94]

why didn't you recommend leaving the death capacitor out of the circuit?

[@timothymatthews4399]

great video!!! Very helpful to learn this simple foundational circuit. There are a couple of sections I hope you can give me clarification on, but maybe off of this string to reduce clutter. I'm interested in getting a little more wattage out of this amp circuit. I built a mojotone 5F1 kit so I feel it's OK to alter the circuit. I can't leave well enough alone and these mods help to learn the circuitry that much more. I've read that a 6L6 can be run in the power amp instead of the stock 6V6. To utilize the 6V6 power handling, a 15W output transformer should be installed. Has anyone tried this? I popped an Eminence 820H 4 Ohm 8" speaker into the cabinet. It sounds great, but would be cool to feed it more "juice". Any advice on that mod?

[@KleyDeJong]

You certainly can put in a 6L6 power tube. A higher powered OT would be important. You may also need to tweak some of the components on the power tube to properly bias the 6L6, specifically the cathode bias resistor. The power transformer should be okay, but something to look into. Can yours handle the current draw? Is the plate voltage optimal? I know something like an EL34 draws a lot more current. A 6l6 may be fine yet. Plate voltage tends to be a bit hot in a 5f1 with 6v6 due to the wall voltage being a bit higher than 1950. But something to look into.

[@freddybeebop6756]

Reminds me of the time I bought a silverface champ at a small music store. As I was leaving, I asked the owner/sales guy how to make it louder. He said 'put it on top of a Marshall'.

[@Blueguitar007]

Nice video - good work. But all those mods increase gain. Why would you want more on a Tweed Champ?

[@Pharesm]

Is this one suitable for a conversion from AC power to DC 12V...?

[@silasfatchett7380]

No.

[@facundorodriguez288]

Hello, we want to build an amp my brother and this video will certanly be helpfull. One question, how many ohms should the speaker be rated at? Thanks!

[@killerbietje]

That will depend on your output transformer. The original champ had a 4ohm OT i believe (or even 3,2). Many modern kits come with a 8ohm OT or an OT that can be used to build multiple outputs (4-8-16). So you should refer to the manual of your output transformer to know what ohm it is made for.

[@Blueguitar007]

4 ohm 8" is the norm. Not many choices, I like the Weber Alnico or Ceramic, ceramic may be optimal for an already gain fuzzy amp. Either will do.

[@ListentoKadence]

Would it be possible for a Champ Amp to be modified to allow an 8 ohm speaker?

[@KleyDeJong]

Yes. Ideally you replace with a proper output transformer.

[@ertreri]

at 4:06 the input 2 seems to be wired in parallel to the same resistor of input 1 i do not see the difference between input 1 and 2. both seem to be equivalent

[@KleyDeJong]

The input jack that is typically used is a 'shorting' type jack. This means that the tip is grounded when nothing is plugged in. So when you plug in a 1/4" cable it lifts that sleeve connection.

[@bluesman5049]

Will it be okay if a 5Y3 rectifier is put in place of 5AR4. In my clone Champ 5F1 is 5AR4.

[@KleyDeJong]

Yes you may do that. You would get more voltage drop with a 5Y3.

[@bluesman5049]

Thanks for your reply. As it reflects on the tone of the amplifier, does it get a lighter tone with less gain.

[@pe4o243]

What can you do to make it more Europe friendly? Outlets here spit a nice 240V, so i think it will make a difference and a half. Also, how can you mod it so the mids are boosted and most highs are removed?

[@KleyDeJong]

The primary side of the Power Transformer needs to have a 240v tap and be wired accordingly. You can add some tone controls no problem. The most commonly used tone stacks in tube amps are passive (they only remove frequencies). So you can't really 'boost'. Rather you are cutting frequencies. The 5F2A has a simple high end roll off tone control. To create a mid 'boost' you would need to cut the highs and bass.

[@pe4o243]

@@KleyDeJong Which one is the tone control on the Princeton? The 1meg that goes to a .005 cap or the other one?

[@ianaintsaying1625]

Why do I see discrepancies in the 5F1's schematic online? Some show a 1.5k connected to pin 5 of the 6V6. Others show a 470Ω resistor between pin 4 and the 2nd filter cap. Other schematics don't even show these components. Why is that?

[@zachary963]

Probably because schematics are made by people reverse-engineering the amp, and may or may not have factory parts or mods in the schematic. Also, sometimes a product name can apply to wildly different products, so a Champ from one year may look very different to a Champ from a later year.

[@Periskop1]

The filter caps are rated 450 volts.Tweed champs run at lower voltages.

[@soundserviceelectronics2083]

No they don't. I have a totally original 1957 5F1 on the bench right now. The idle output tube current is a bit high due to other issues common to these amps with all original parts and the filters aren't in the greatest shape which tends to pull the B+ down a bit. The B+ at the first filter is 384V at 110 V AC Line (The original intended line AC voltage). At 120V AC Line the first node is at 419V DC. That makes things really hot for the output tube. This is why 'browners' are highly recommended, get a UL / CE / CSA approved one though, for Tweed Fender amps. The AC line voltage was lower in the mid to late 50s. Filter caps in an amp are subject to crest voltage when the amp is first turned on until the tubes warm up. This crest exceeds 477V DC. The caps can handle this because they are rated for 525V surge for a short time. Do not reduce ratings. Do not use import caps in these. Offshore caps have no additional surge rating.

[@manoel123123]

Thanks man. I recently bought a Monoprice 15W tube amp. And I think there is too much low end. I will play with some coupling capacitors/bypass capacitors, and see if I can get a tighter tone!

[@Blueguitar007]

Isn't that going to be a PCB? That's more difficult to change things.

[@marsattacks7071]

Great explanations ! You say that the 6V6GT is a pentode but according to the drawing, it looks like a tetrode. Is that possible ?

[@southerner66]

6V6s and 6L6s are technically "beam tetrodes" as opposed to "true pentodes" like the EL34, but the two terms get mixed up, partly because there's some crossover equivalence. For example, the American 6CA7 was a beam tetrode, but can be subbed for an EL34, which is a pentode. In a beam tetrode, the beam-forming plates take the place of the pentode suppressor grid.

[@Blueguitar007]

@@southerner66 Spock... We need you on the bridge ASAP!

[@stephenchung]

what is the plate voltage?

[@daveb9370]

They are listed on the schematic. Resistors are used to decrease the voltages thru the circuit. Plate voltages are marked B+ which comes from the power transformer. B+ comes from old amps that ran on batteries.

[@avit719]

what is saddering?

[@silasfatchett7380]

It's the North American pronunciation of 'soldering'.

[@squidkid2]

One thing that you didn't address is the death capacitor. Anyone who is new to high voltage tube circuits needs to really understand the importance of a chassis ground. As you can see by this schematic there is no chassis ground. If you bought one of these amps back in the day you got a 2-wire power cord. That's the hot and the neutral wires. In fact your wall outlet back then only had two holes. All modern wall sockets have 3 holes. The third hole in the one that carries the ground wire. If you look at a modern power cord it has a black wire a white wire and the third wire is green for ground. If any high voltage wire comes loose inside the amp and touches the chassis then if you touch that hot chassis you will get a high voltage shock. The green wire is connected to the chassis so that if a high voltage wire inside the amp touches the chassis there is a high current short that goes down the green wire back to the circuit breaker in the main panel in your house and immediately trips the circuit breaker in your house and shuts off power to the wall outlet. The death cap was there to control voltage surges when the main on-off switch is first turned on. But that cap can fail and provide a direct path for line voltage to the chassis and without the chassis ground there is no way for the circuit breaker to see a high current and trip. So you need to install a 3 wire power cord and delete the cap in the schematic that is right by the power fuse.

[@eksund1900]

Just found this video. Apart from some minor "hickups" I like what a see. Most obviolus is the explanation you give at 4:50. The two input is not behaving like. If using input 1 the signal goes over both the 68k resistors giving 34k. But if using input 2 only one 68k resistor effekt the signal. So as you said earlier in the video the two input act:s like a hi/lo input.

[@christopheraustin8827]

Eliminating your negative feedback in the way you suggested can cook your transformer! Be careful!

[@ALEXONLIFE]

Do you have a schematic for the proper way to do it? I am about to do this negative feedback mod and would like to use the best method. Would be appreciated.

[@cgmasterman]

At13:23 you say nice 120 cycle it’s 60 cycle 120 volts

[@cgmasterman]

At 12:21 you said pentode tube it is not it’s a tetrode tube😎🤪

[@timothygrupp]

No comment...

[@teleguy2650]

u F ? kind of scary that you dont know what a microfarad is. There are some parts of the circuit that you are either clueless about or maybe not able to describe in correct terminology. Good effort.

[@stevesteiner9472]

It's like "Oh Ess Ex" for Mac OS X. I think it's the curse of the autodidact.

[@stevesteiner9472]

And, do you have a better explainer somewhere?

[@Spentelectrons]

@@stevesteiner9472 uncle doug how tube amplifiers work

[@kubockferre5532]

hi,id like to know what the secondary voltage of the power transformer and voltage on the 6v6 plate and voltage on the 12ax7 plate cause voltage is not there on this shematic thanks