Building My First Tube Amplifier

[Eternalvoid]

Recently my old Marantz 2220B died, although it was not the world's highest quality or most impressive receiver. I enjoyed it greatly and was very pleased with it. I am a student currently studying electrical engineering technology and was able to obtain said receiver in nonworking condition. I originally was able to repair the receiver, however this time I have been unsuccessful. I have recently been interested in designing and building my own tube amplifier. I have in mind something using some 12AX7's as signal amplification, and something else as main power amplification. I would like some help with the following.
1) what would be a good tube choice for main power amplification?
2) What power transformer do you recommend to go along with said tubes? (I have been looking at the Tube Depot 6G15)
3) What output transformer would you advise? (I was considering the Hammond Manufacturing 1760CP)
I overall am unsure of the compatibility of the options I have been considering, and would like advising. I greatly appreciate all the assistance provided.

 

[egellings]

1) How many watts output do you want form the amplifier. 6V6 makes for sweet PP 10 watt or so amps. 6BQ5/EL84 is good for up to 15 PP watts, EL34/6CA7 or maybe a nice 6L6 is good for about 35 PP watts. 6550 or KT88 types and larger can do 60 PP watts or more. "PP" means push-pull, or two tubes used in the output section operated in push-pull fashion. Not familiar with single ended operation for these tubes.

 

[Binkman]

Welcome to A.k.
You have quite a wish list. However I"m not knocking building your own equipment as many do build. Perhaps better experience would be repair the Marantz and understand that better. Why not post what issues you can't resolve up here on DIY?? Or SS forum?
Restored Marantz usually brings a good buck return... might be able to buy some equipment.

 

[Lavane]

There are some very nice kits available as well. Both single ended and push pull. Don't restrict yourself to just the 12AX7. Also, are you wanting to build from scratch point to point, or kit? I've built a couple amps starting with nothing more than a blank PCB and BOM, and choose your own brands of components, chassis, etc. Lots of lanes on this highway to drive down.

 

[Eternalvoid]

1) How many watts output do you want form the amplifier. 6V6 makes for sweet PP 10 watt or so amps. 6BQ5/EL84 is good for up to 15 PP watts, EL34/6CA7 or maybe a nice 6L6 is good for about 35 PP watts. 6550 or KT88 types and larger can do 60 PP watts or more. "PP" means push-pull, or two tubes used in the output section operated in push-pull fashion. Not familiar with single ended operation for these tubes.

I'm thinking ten watts, I am glad you asked. As I originally had not considered wattage. I am leaning towards a single-ended amplifier for my first build, however am open to push-pull. I'm definitely going to look into the 6V6. Thank you.

 

[Eternalvoid]

Welcome to A.k.
You have quite a wish list. However I"m not knocking building your own equipment as many do build. Perhaps better experience would be repair the Marantz and understand that better. Why not post what issues you can't resolve up here on DIY?? Or SS forum?
Restored Marantz usually brings a good buck return... might be able to buy some equipment.

I am very open to repairing the Marantz, I may work on repairing it while I develop a design for my tube amplifier. It was originally given to me in non-working order. And required a new power cord, and main filter capacitors to operate. I am currently unsure as to why it is not operating. When powered on, the display illuminates however no audio output is present on either the main or remote speakers. I tried all inputs with no success. Thank you for the advice

 

[Eternalvoid]

There are some very nice kits available as well. Both single ended and push pull. Don't restrict yourself to just the 12AX7. Also, are you wanting to build from scratch point to point, or kit? I've built a couple amps starting with nothing more than a blank PCB and BOM, and choose your own brands of components, chassis, etc. Lots of lanes on this highway to drive down.

I would really like to start from scratch, I enjoy the challenge of learning and being able to modify things to do what I would like. That said, I have lots of learning to do before I am fully able to design an amp. The reason I would like to implement the 12AX7 is I have a surplus of them manufactured by Ratheon. WIth this project being in its early stages, I am very open to using other tubes. Thank you for the feedback

 

[grindfix]

Look at this monster thread by tube guru here. This amp can be built from scratch choosing your transformers and chassis design. Circuit design is proven masterpiece! It sounds really, really good! Better then most small amps I've heard. Ticket is to use efficient speakers matched to it's impedance
https://www.audiokarma.org/forums/i...ore-out-of-the-8600-series-a-lot-more.665735/

And, welcome to AK!
Visit Tube Forum for more ideas too!

 

[Binkman]

I am currently unsure as to why it is not operating. When powered on, the display illuminates however no audio output is present on either the main or remote speakers. I tried all inputs with no success.

How far ahead are you in measurement experience? Have a DMM and know how to measure circuits? I'm not familiar with Marantz in general as they're usually kept by owners in NC. Rarely for sale. However there are many members that are experienced. Your issue may be as simple as the speaker relay but could be more to it.

Service user manuals:
https://www.hifiengine.com/manual_library/marantz/2220.shtml

Service manual errors top of 1st post.
https://audiokarma.org/forums/index.php?threads/marantz-service-manual-error-thread.375907/
2220B Idle current adjust:
SM says measure J712 - 718 for one channel, 713 to 719 for the other. WRONG! Do this instead: Measure bias at J714 to 716 and adjust R733 for 20mVDC on that channel. Then measure J715 to 717 and adjust R734 for 20mV on the other channel.

2220B Cap listing:
Service manual lists CE21 & CE22 as 33 uF/50v. Should be 3.3 uf/50v.
CE23 & CE24 listed as standard 1.0 uF/50V. Use non polar caps here.
C709 and C710 should be 47uf 50V, not the listed 500V.

2220B Forum search results (top right search pane)
https://audiokarma.org/forums/index.php?search/56220118/&q=marantz+2220b&o=date

 

[trainbuftony]

A bit of advice, from a starving student type.
Dont spend gobs of money on parts for the first one. Don't pretend for a second that your first one will be your last. It's a prototype, a stepping stone. Once you learn the lessons your first amp has to teach you, you'll have all sorts of new ideas for the next one. You don't need boutique caps western electric transformers or anything fancy to build an extremely solid 6v6 poweramp dont let anyone convince you otherwise.
Learn to build a solid circuit through prototyping, and when the time comes for trick chassis, boutique caps, andwalnut cases, you will have a circuit worthy of the bling.

If you ever have any questions don't hesitate to ask.

 

[Eternalvoid]

How far ahead are you in measurement experience? Have a DMM and know how to measure circuits? I'm not familiar with Marantz in general as they're usually kept by owners in NC. Rarely for sale. However there are many members that are experienced. Your issue may be as simple as the speaker relay but could be more to it.

Service user manuals:
https://www.hifiengine.com/manual_library/marantz/2220.shtml

Service manual errors top of 1st post.
https://audiokarma.org/forums/index.php?threads/marantz-service-manual-error-thread.375907/
2220B Idle current adjust:
SM says measure J712 - 718 for one channel, 713 to 719 for the other. WRONG! Do this instead: Measure bias at J714 to 716 and adjust R733 for 20mVDC on that channel. Then measure J715 to 717 and adjust R734 for 20mV on the other channel.

2220B Cap listing:
Service manual lists CE21 & CE22 as 33 uF/50v. Should be 3.3 uf/50v.
CE23 & CE24 listed as standard 1.0 uF/50V. Use non polar caps here.
C709 and C710 should be 47uf 50V, not the listed 500V.

2220B Forum search results (top right search pane)
https://audiokarma.org/forums/index.php?search/56220118/&q=marantz+2220b&o=date

I will look through those manuals and soon start measuring. I have a personal DMM and other basic electrical tools. I also have access to a full electrical lab through my university.

 

[Eternalvoid]

A bit of advice, from a starving student type.
Dont spend gobs of money on parts for the first one. Don't pretend for a second that your first one will be your last. It's a prototype, a stepping stone. Once you learn the lessons your first amp has to teach you, you'll have all sorts of new ideas for the next one. You don't need boutique caps western electric transformers or anything fancy to build an extremely solid 6v6 poweramp dont let anyone convince you otherwise.
Learn to build a solid circuit through prototyping, and when the time comes for trick chassis, boutique caps, andwalnut cases, you will have a circuit worthy of the bling.

If you ever have any questions don't hesitate to ask.

I appreciate the solid advice, with my current idea I am putting great emphasis on learning and minimizing expense. Earlier today I was given a "Parts" radio that I intend to harvest sockets and other components from that are useable. Of course, capacitors and other components that are no longer viable will not be harvested. I greatly respect how everyone is so willing to provide assistance.

 

[Lavane]

You could ask to have this thread moved to the Tube Forum. There are people that have built some very nice amplifiers and can suggest schematics for a first build.
You should nail down the kind of output power your looking for first.

A bit of advice, from a starving student type.
Dont spend gobs of money on parts for the first one. Don't pretend for a second that your first one will be your last. It's a prototype, a stepping stone. Once you learn the lessons your first amp has to teach you, you'll have all sorts of new ideas for the next one. You don't need boutique caps western electric transformers or anything fancy to build an extremely solid 6v6 poweramp dont let anyone convince you otherwise.
Learn to build a solid circuit through prototyping, and when the time comes for trick chassis, boutique caps, andwalnut cases, you will have a circuit worthy of the bling.

If you ever have any questions don't hesitate to ask.

^^This^^ My first amp build was a 6V6 Magnavox 175 chassis pulled from an old console. While not a scratch build, much must be replaced, electrolytic and film caps and I found many of the old carbon comp. resistors had drifted. I replaced all the resistors, caps, split the cathodes, changed the coupling cap values for better low end and rewired it for stand alone use along with wrapping the chassis in some nice wood. You can take it further and replace the output transformers with some nice Edcor output trany's too. A console pull can be a great way to start in tubes. You do learn a thing or two along the way. The Magnavox 175, 185 and 93xx chassis are all between 10-12wpc.

 

[Eternalvoid]

Update, I think I have decided on what I am going to use. However, included in my parts list are Edcor transformers. Meaning, I will have 10 weeks to fill. For power I am considering an Edcor XPWR001, Output two Edcor WSE10-5k. A single 12AX7 for signal amplification, and two 6V6GT for power amplification. In the meanwhile, I will patiently refine my design and understanding. While also working to repair my Marantz. I appreciate all the great input and assistance I have been given. I may change my other mind about the edcor transformers depending on f I find a decent alternative that does not preset the great lead time.

 

[Lavane]

Do you have a schematic to work with yet?

 

[Eternalvoid]

Do you have a schematic to work with yet?

Not yet, I will create one after work tomorrow. I'm needing to do more research on calculating cathode bias resistors and capacitors, along with coupling capacitors. I will keep you posted. Thank you

 

[Binkman]

Don't forget the little stuff.. like, chassis mods, (tube vent covers), Rca connectors, perhaps solder trees, wire colors, wire wraps, power LED or illuminated power switch? Maybe throw in a headphone circuit.
Tube source selection.. A russian 12AX7 may give a better sound.

 

[Eternalvoid]

Don't forget the little stuff.. like, chassis mods, (tube vent covers), Rca connectors, perhaps solder trees, wire colors, wire wraps, power LED or illuminated power switch? Maybe throw in a headphone circuit.
Tube source selection.. A Russian 12AX7 may give a better sound.

I like the headphone idea, I have an illuminated switch on hand I planned to use. Also, for the 12AX7 I have several options on hand including, RCA, Raytheon, and GE. Should I order a Russian tube? Or would one of those compare?

 

[Binkman]

You have stock on hand and want to keep costs down.

 

[gadget73]

If you can scare up an amp chassis to rebuild around that would generally cut the prices a fair bit. Console stereo amps used to be the common entry point as either a rebuild or a platform to re-engineer but they have gotten more spendy. They still make a good value in terms of parts and a chassis even if you gut the electronics and start over with a new design. If you're going that route, have a gander at the schematic first before picking one. I'd avoid 3 channel stuff and ones with those wierd mono/stereo all in one deals. You want something that is 2 basically identical channels using the same power tubes and transformers on each channel. That gives you 2 identical sets of parts to work with in order to build a "normal" stereo amp.

two matching mono amps also work fine but unless you can get both at once I've found trying to play mix and match with mono amps to be a real pain in the neck. Also it seems like the second one costs many times as much as the first one. Mono amps make good guitar amp projects if you're into that though. PA amps with lots of knobs are especially handy, even if you gut the circuit you have a panel with controls on it.

also avoid anything that does not use a power transformer. They're dangerous for one but the output transformers tend to be not so useful for much beyond what they were originally connected to. I'd be aiming for stuff that uses common tubes, 6V6 and 6BQ5 are probably what you're most likely to find in a US-made console amp at least.