Good to know if you have a few low wattage valve amps that distort quickly, to get more clean headroom out of it, esp if it is a single channel amp! KEEP it clean, & use a dirt box in the front of it! Orange Tremlord 30 springs to mind! Totally clean, 50's style amp, but with modern appointments like spring reverb, tremolo circuit and an effects loop!
i think the original design idea back in the 60's was that you plug both a bass guitar and a guitar into the same amp but in all reality that would suck big time. I know when they built the marshall plexi the idea was to have the singer in there also. lolz
That was insightful. I’ve been wondering about this. My 55’ Maestro GA 45 has a completely different input resistance than the famed G-40 which in almost every other way is the same bar a separate bass and treble pots. I’m going to test this tomorrow.
With a typical guitar pickup impedance being around 10K, amp input impedance of 130k doesn't load it significantly more than 1M, the difference would be even less when testing with a signal generator, as it has minimal output impedance. The observed difference in gain is because of the fact that in the original circuit, the two 68k resistors were forming a 1:2 voltage divider. Adding a 1M resistor at the bottom effectively turns it into a 19:20 divider or thereabouts. Plus, you bypassed the cathode resistor of the input stage.
Ch 2 has the cathode to ground, and it is NOT grid biased. The low plate voltage allows for this. I changed my Ch 2 on mine to "normal" on the cathode.
Hi Terry. Hope this note find you and yours and Extended family happy and healthy. Congrats! Nice touch sending the guitologiguy a new glass. I hope Uncle Doug is next. What is the best way to reach out to you? I would like for you to take a look at a schematic for me for a fee of course.
Very cool! Thank you! I'm about to design a preamp like this, although I'm wondering about using an EF86 - I suppose I'd have to use two; one for the guitar input and one for the MP3 player. Either that or install a switch. Love your videos, btw. Very clear. I learn a lot.
Love these videos . I've learned a good bit from them. You should get you a cheap guitar and just learn how to tune it and play a couple of chords for comparison when modifying amps. If not , oh well. I'm just a guitar nerd and thought I'd throw out a suggestion. Keep up the good work, thanks.
Very Cool Terry! Along those thoughts... What if I wanted to run a microphone into the Normal Channel on my Vibrolux Reverb, what impedance Mic. should I look for?
Draw up the mods on a 3x5 card and paste inside the cabinet. I'd also try to error proof the input jacks somehow so the mp3 doesn't get put in channel one (maybe swap the 1/4in jack for 1/8th inch). Decal for the MP3 jack? Pretty important kind of mod -- maybe a follow up generic method to doing this on any amp? Perhaps a potentiometer instead of fixed resistors?
So Terry, how much distortion will the owner now get from the change in the Fender type input? You said the owner liked the original inputs because she could turn up the volume and have clean tone all the way up. That would be ideal for say a bass guitar amp. Just wondering.....Great new video. Love Dlab! Thanxz
I have a question for you. I have 2 stancor A-3872 output transformers Input 5000 ohms c.t. outputs 4, 8, and 16 ohms. My question is if use the the 4 ohm tap with a 8 ohm speaker or the 8 ohm tap with a 16 ohm speaker can the input now be used as a 10k ohm c.t. input for either push-pull 6V6s or 6BQ5s?
Hello, I have not played with the bluetooth modules. If they have an analog (audio) output, you could make an adapter cable, then plug into the amp. The MP3 players have a volume control, so it can be throttled for the correct level. Does bluetooth have that?
@@d-labelectronics Hello Terry, I'm not sure, but if one is Bluetoothing from a phone to the amp then the volume control on the phone comes into play. I'm currently playing guitar through a Eico 147A signal tracer. I changed the RF input Jack to a 1/4" Jack and replaced the original speaker with a eminence. Sounds pretty sweat. So I'm making a clone and I want to add Bluetooth instead of aux in. So many wires... Thanks! Dan.
Is there any chance, that you could help a youtuber from the channel *realbeal* ? She has an old Fender amp, that makes terrible noise lately. the video called "What is Wrong with my Bass Amp?"
You don't get it. "Intinuation" is a portmanteau between attenuation and insinuation. So if someone comes to you and says "You've lost credibility", you can reply, "What are you intinuating?" See? That's a nice way to declutter your dictionary, with all those unnecessary words.
Your in-depth knowledge of how to work on these amps is astounding my friend !!
Terry, great idea putting the MP3 in the second channel. I can't wait to get this amp back and start annoying the neighbors. 😀
There ya go wanting piss off the neighbors again!
@@stepvanjoe3469 Gonna crank it up to 11! 🤣
Good to know if you have a few low wattage valve amps that distort quickly, to get more clean headroom out of it, esp if it is a single channel amp! KEEP it clean, & use a dirt box in the front of it! Orange Tremlord 30 springs to mind! Totally clean, 50's style amp, but with modern appointments like spring reverb, tremolo circuit and an effects loop!
i think the original design idea back in the 60's was that you plug both a bass guitar and a guitar into the same amp but in all reality that would suck big time. I know when they built the marshall plexi the idea was to have the singer in there also. lolz
Absolutely Brilliant, Terry! I love that you gave another purpose to this old classic.
Good stuff Terry it is surprising sometimes how easy these mods can be that are sold as features on new amps.
Cool vid, let us know how the client likes the 'new' amp!
That was insightful. I’ve been wondering about this. My 55’ Maestro GA 45 has a completely different input resistance than the famed G-40 which in almost every other way is the same bar a separate bass and treble pots. I’m going to test this tomorrow.
With a typical guitar pickup impedance being around 10K, amp input impedance of 130k doesn't load it significantly more than 1M, the difference would be even less when testing with a signal generator, as it has minimal output impedance.
The observed difference in gain is because of the fact that in the original circuit, the two 68k resistors were forming a 1:2 voltage divider. Adding a 1M resistor at the bottom effectively turns it into a 19:20 divider or thereabouts. Plus, you bypassed the cathode resistor of the input stage.
Great tips Terry.... that really helps explain how the input channels work for me.... very very good and thank you very much my friend.... awesome
Excellent Sir. Great hobby. I'm putting the wraps on this project. Next video will feature it being played
Excellent video, Terry. Love the MP3 mod. By chance, have you done a vidya showing how to install a mute switch? I haven't seen one in your catalog.
Ch 2 has the cathode to ground, and it is NOT grid biased. The low plate voltage allows for this. I changed my Ch 2 on mine to "normal" on the cathode.
Hi Terry. Hope this note find you and yours and Extended family happy and healthy. Congrats! Nice touch sending the guitologiguy a new glass. I hope Uncle Doug is next. What is the best way to reach out to you? I would like for you to take a look at a schematic for me for a fee of course.
Very cool! Thank you! I'm about to design a preamp like this, although I'm wondering about using an EF86 - I suppose I'd have to use two; one for the guitar input and one for the MP3 player. Either that or install a switch. Love your videos, btw. Very clear. I learn a lot.
The lower value resistor and the capacitor are techniques to reduce radio detection by amplifiers.
Another great video Terry
Great tek-tip Terry. Say that five times real fast.Hahaha.👍🎸
"Terrific Tek-tip Terry"... :-)
Great stuff Terry!
Clever!
Love these videos . I've learned a good bit from them. You should get you a cheap guitar and just learn how to tune it and play a couple of chords for comparison when modifying amps. If not , oh well. I'm just a guitar nerd and thought I'd throw out a suggestion. Keep up the good work, thanks.
Yes Sir. I do have a Telecaster, just can't play! Maybe I can learn the instrument when I retire form the day job
@@d-labelectronics - just a few chords would do it.
Very Cool Terry!
Along those thoughts... What if I wanted to run a microphone into the Normal Channel on my Vibrolux Reverb, what impedance Mic. should I look for?
Superb idea and mod .
Bless you for sharing your wisdom with us!!!
Excellent !! Thank You !!
Draw up the mods on a 3x5 card and paste inside the cabinet. I'd also try to error proof the input jacks somehow so the mp3 doesn't get put in channel one (maybe swap the 1/4in jack for 1/8th inch). Decal for the MP3 jack? Pretty important kind of mod -- maybe a follow up generic method to doing this on any amp? Perhaps a potentiometer instead of fixed resistors?
Nice tip and thanks
Nice!! Thanks for the Input.... :-)
Your being over sensitive!
So Terry, how much distortion will the owner now get from the change in the Fender type input? You said the owner liked the original inputs because she could turn up the volume and have clean tone all the way up. That would be ideal for say a bass guitar amp. Just wondering.....Great new video. Love Dlab! Thanxz
Good point, not sure. Will have her demo the amp when complete. Hopefully its the sound she's after
I have a question for you. I have 2 stancor A-3872 output transformers Input 5000 ohms c.t. outputs 4, 8, and 16 ohms. My question is if use the the 4 ohm tap with a 8 ohm speaker or the 8 ohm tap with a 16 ohm speaker can the input now be used as a 10k ohm c.t. input for either push-pull 6V6s or 6BQ5s?
I wondered do MP3 and other computer audio sound good when amplified by a tube amplifier? How does it sound in comparison to solid state?
Why doesn´t the MP3-Input have a cathode resistor? Wouldn´t it be a good idea to add also 1.5k at pin 3 without parallel capacitor to reduce gain?
I tried to keep the mod very basic. Im sure there would be many improvements to the MP3 channel
where are you located? any where near MN?
Nice mod!!!
Can you show the modified circuit?
What happened to the 1 meg ohm from grid to ground on input 1. I saw only the two 68k resistors.
It is on the input jack, same as how Fender does it
Any advice regarding Bluetooth mod? Thanks! Great channel!
Hello, I have not played with the bluetooth modules. If they have an analog (audio) output, you could make an adapter cable, then plug into the amp. The MP3 players have a volume control, so it can be throttled for the correct level. Does bluetooth have that?
@@d-labelectronics Hello Terry, I'm not sure, but if one is Bluetoothing from a phone to the amp then the volume control on the phone comes into play. I'm currently playing guitar through a Eico 147A signal tracer. I changed the RF input Jack to a 1/4" Jack and replaced the original speaker with a eminence. Sounds pretty sweat. So I'm making a clone and I want to add Bluetooth instead of aux in. So many wires... Thanks! Dan.
Is there any chance, that you could help a youtuber from the channel *realbeal* ?
She has an old Fender amp, that makes terrible noise lately.
the video called "What is Wrong with my Bass Amp?"
"Attenuate" please...I really like your videos, but you lose credibility when the terms are pronounced incorrectly
Yes, I see. Guess I should only wear collared shirts too.
@@d-labelectronics Not at all...everything else about your videos is great. I've been watching for years.
Excellent, just playing around my friend, Glad to have you on board. TD
You don't get it. "Intinuation" is a portmanteau between attenuation and insinuation. So if someone comes to you and says "You've lost credibility", you can reply, "What are you intinuating?" See? That's a nice way to declutter your dictionary, with all those unnecessary words.
@@sextoempirico2243 LMAO, perfect! I love it 😂