[tomb]

Thanks for the info, very interesting.

I'd love to try some Lundhahls.. I have been looking at their website and they only seem to list 3 headphone specific models, none with an input impedance of 10k and suitable secondaries. I think I could try and work it out with respect to turns ratio but I'm not sure how close they would be, I also have limited knowledge in this field so aren't that confident. The Papa Rusa design specifies "The various (secondary tap) configurations allow for about an 8k load with 32 ohms, a 20k load with 300 ohms, and everywhere in between with other headphones.". I also noticed that the way they have secondaries set up I'm not sure how easy it would be to have switchable secondary taps, do you have to just wire it for one specific impedance?

That leaves the Cinemags, I see that the CM-15615PC is a custom order, maybe I could just order these? Are there any published specs with info on secondary taps etc?

Please forgive all my novice questions, this is really the first tube amp I've built from a schematic by myself.

The last time I talked to Cinemag, or had someone follow my recommendation to purchase them, Cinemag had no issue winding just two for a customer. Transformer mfrs (including Edcor) tend to be OK with that, as long as the part # is something they've already produced. Getting them to wind custom transformers that they've never done before is usually much more expensive and requires a volume purchase, most likely.

They should be able to make those CM-1561PC pair for you without much issue. You just call them up, discuss what you want, and give them a credit card #. You can ask them any questions while you're at it. You might ask for David, if he's still there and mention that they were for ECP/Beezar Audio's T3 (Torpedo III) amplifier. The CM-1561PC has two output windings (optimized for low and high impedance) that can be controlled with a simple DPDT switch on the output. Unfortunately, I don't seem to have an actual schematic in my files, but Doug Savitsky made them as an exact replacement for the Edcor PCW10K-7K/300-32 (used on the Torpedo I). They can be found here: https://edcorusa.com/products/pcw-1...1&_sid=2581b6de7&_ss=r&variant=41236729200827. So, if you order the Cinemags, they'll be the same (electrically) as the Edcors. The difference is the Cinemags were a bit taller - can't remember how much, maybe 1/2" - 3/4" taller.

Lundahl is a different animal altogether. They have exclusive distributors that they work through and typically do large batch manufacturing for catalog stock items only once a year. They'll still pretty much custom wind whatever you want, as long as you order 50 of them. They're definitely better than either the Cinemags or Edcors, but probably not as much difference as between the Cinemags and Edcors. Trying to put numbers to subjective listening, it's sort of like the Cinemags are 50% better than the Edcors, while the Lundahls are 20% better than the Cinemags, if that even makes sense.

Doug had a number of them leftover from our T4 builds and sales. The thing to do - if you want to try the Lundahls - is send Doug a PM here on Head-Fi (user account: dsavitsk). Ask him if he still has a pair of the T4 Lundahls and if he'd sell them to you. The Lundahl is electrically identical to the Edcor and Cinemags, but output impedance for the low Z winding is a bit higher (50 ohms optimization, if I remember correctly). Besides quality, the Lundahls also have a very low DC resistance compared to either the Cinemags or Edcors, which is important for low impedance headphones. DC resistance tends to govern with low impedance loads. At least that's what I understand from conversations with Doug.

 

[Sonic Defender]

I am so impressed with everything about this thread. First up the lovely build story. I found it fascinating to see things unfold and the final product is understated and beautiful. What a pleasure it must be to have the various skills and such a complete workshop. My father would be in heaven in such a space.

I also really like how others with knowledge to share joined in and selflessly shared their time and advice. This in my mind is the best of head-fi as a community on display. Great read and I look forward to following the thread.

 

[Jerm111]

The last time I talked to Cinemag, or had someone follow my recommendation to purchase them, Cinemag had no issue winding just two for a customer. Transformer mfrs (including Edcor) tend to be OK with that, as long as the part # is something they've already produced. Getting them to wind custom transformers that they've never done before is usually much more expensive and requires a volume purchase, most likely.

They should be able to make those CM-1561PC pair for you without much issue. You just call them up, discuss what you want, and give them a credit card #. You can ask them any questions while you're at it. You might ask for David, if he's still there and mention that they were for ECP/Beezar Audio's T3 (Torpedo III) amplifier. The CM-1561PC has two output windings (optimized for low and high impedance) that can be controlled with a simple DPDT switch on the output. Unfortunately, I don't seem to have an actual schematic in my files, but Doug Savitsky made them as an exact replacement for the Edcor PCW10K-7K/300-32 (used on the Torpedo I). They can be found here: https://edcorusa.com/products/pcw-1...1&_sid=2581b6de7&_ss=r&variant=41236729200827. So, if you order the Cinemags, they'll be the same (electrically) as the Edcors. The difference is the Cinemags were a bit taller - can't remember how much, maybe 1/2" - 3/4" taller.

Lundahl is a different animal altogether. They have exclusive distributors that they work through and typically do large batch manufacturing for catalog stock items only once a year. They'll still pretty much custom wind whatever you want, as long as you order 50 of them. They're definitely better than either the Cinemags or Edcors, but probably not as much difference as between the Cinemags and Edcors. Trying to put numbers to subjective listening, it's sort of like the Cinemags are 50% better than the Edcors, while the Lundahls are 20% better than the Cinemags, if that even makes sense.

Doug had a number of them leftover from our T4 builds and sales. The thing to do - if you want to try the Lundahls - is send Doug a PM here on Head-Fi (user account: dsavitsk). Ask him if he still has a pair of the T4 Lundahls and if he'd sell them to you. The Lundahl is electrically identical to the Edcor and Cinemags, but output impedance for the low Z winding is a bit higher (50 ohms optimization, if I remember correctly). Besides quality, the Lundahls also have a very low DC resistance compared to either the Cinemags or Edcors, which is important for low impedance headphones. DC resistance tends to govern with low impedance loads. At least that's what I understand from conversations with Doug.

Thanks so much for the detailed run-down.

I haven't had time to have a good listen or a decent comparison with my other amps but my first impression is that this amp sounds very good. This talk of improved transformers has me very intrigued at what the potential could be though.

I will see what Doug has to say.

I am so impressed with everything about this thread. First up the lovely build story. I found it fascinating to see things unfold and the final product is understated and beautiful. What a pleasure it must be to have the various skills and such a complete workshop. My father would be in heaven in such a space.

I also really like how others with knowledge to share joined in and selflessly shared their time and advice. This in my mind is the best of head-fi as a community on display. Great read and I look forward to following the thread.

Thanks! I agree, I'm very grateful when anyone is forthcoming with knowledge and willing to take the time to explain and educate. In turn I am always willing to offer my advice on where possible.

I am fortunate to be employed at a workplace where I have access to very extensive prototyping workshops. My home workshop has been several years in the making, reinvesting money from various odd jobs etc.

Here is a picture of that amp almost completed, I'm just waiting for some screws to attach the top plate.

 

[tomb]

Beautiful!

 

[Sonic Defender]

I enjoyed reading your DIY bandsaw project. Fantastic work.

 

[Sonic Defender]

Thanks so much for the detailed run-down.

I haven't had time to have a good listen or a decent comparison with my other amps but my first impression is that this amp sounds very good. This talk of improved transformers has me very intrigued at what the potential could be though.

I will see what Doug has to say.


Thanks! I agree, I'm very grateful when anyone is forthcoming with knowledge and willing to take the time to explain and educate. In turn I am always willing to offer my advice on where possible.

I am fortunate to be employed at a workplace where I have access to very extensive prototyping workshops. My home workshop has been several years in the making, reinvesting money from various odd jobs etc.

Here is a picture of that amp almost completed, I'm just waiting for some screws to attach the top plate.

Wow, that is simply gorgeous. You must be very proud.

 

[Jerm111]

I enjoyed reading your DIY bandsaw project. Fantastic work.

I'm glad you enjoyed, it was a very satisfying project, a lot more work than I thought though!

 

[Sonic Defender]

I'm glad you enjoyed, it was a very satisfying project, a lot more work than I thought though!

I'll bet it was. Keep up the great work and I hope that you have many more satisfying projects to come yet.

 

[Jerm111]

Here are some photos of the finished amp...

I've run into a technical issue which I was hoping someone on here might be able to clarify for me.

I was measuring he plate voltages and noticed they varied quite a bit between channels, 117V (L) and 153V (R). When I switch the tubes, the voltages follow so I assume this is a mismatch caused by the tubes? The amp sounds very good as-is, should I be trying to source a better matched pair?

I mentioned this somewhere else online and was instructed to check the bias current / cathode resistors...

I've confirmed both of the cathode resistors are 51 ohms as per the schematic (50 ohms) shown below.

The plates are sitting at Left: 117 V, Right 153 V. I've measured the voltage across the left and right cathode resistors, 1.154 V and 1.261 V respectively. This gives me Left: 22.6 mA, Right 24.7 mA. This seems a little low as the tube is rated for 40mA +/-12mA with a 30ohm cathode resistor. I used 51 ohm as that is what is specified in the design but I could reduce the resistance to increase the current slightly but I'm not sure how/if that would effect the plate voltage.

I don't fully understand the theory behind all this, how does bias current relate to the plate voltage and how does the tube mismatch play into it? Any help or advice would be appreciated! I probably need to re-watch a bunch of basic tube theory youtube videos..

 

[itsikhefez]

Echoing all the other comments here, this is a beautiful build, congrats.

I have been looking to build a parafeed HP amp based off of 5842 tube for a while, and more recently acquired some 6C45PI tubes so may build this one instead.
I purchased a pair of Sowter 8665 transformers for the project, but the Cinemag mentioned here is interesting as well.

Did you ever resolve your plate voltage mismatch issue? One way is certainly to have better matched tubes.
Another possibility is to add a trimpot to the cathode resistor, and adjust each tube for the same plate voltage ~150V. Something like replacing the 50ohm resistor to 120ohm with a 180ohm trimpot in parallel.

The plates are sitting at Left: 117 V, Right 153 V. I've measured the voltage across the left and right cathode resistors, 1.154 V and 1.261 V respectively. This gives me Left: 22.6 mA, Right 24.7 mA. This seems a little low as the tube is rated for 40mA +/-12mA with a 30ohm cathode resistor

I'm not sure how this works with the CCS, since it should ensure that the current through the tube is constant at 30mA

 

[Jerm111]

Echoing all the other comments here, this is a beautiful build, congrats.

I have been looking to build a parafeed HP amp based off of 5842 tube for a while, and more recently acquired some 6C45PI tubes so may build this one instead.
I purchased a pair of Sowter 8665 transformers for the project, but the Cinemag mentioned here is interesting as well.

Did you ever resolve your plate voltage mismatch issue? One way is certainly to have better matched tubes.
Another possibility is to add a trimpot to the cathode resistor, and adjust each tube for the same plate voltage ~150V. Something like replacing the 50ohm resistor to 120ohm with a 180ohm trimpot in parallel.


I'm not sure how this works with the CCS, since it should ensure that the current through the tube is constant at 30mA

Thank you.

No I didn't make any more adjustments. I figured I should try and test the tubes I had and probably try sourcing a better matched pair. I inherited a very nice AVO MK4 tube tester but haven't had time to sit down and work out how to use it. I did briefly look into the book and found that the 6C45 tube was not listed, that's as far as I got.

At the end of the day, the amp sounds great and I can't hear the difference...

 

[Jerm111]

Echoing all the other comments here, this is a beautiful build, congrats.

I have been looking to build a parafeed HP amp based off of 5842 tube for a while, and more recently acquired some 6C45PI tubes so may build this one instead.
I purchased a pair of Sowter 8665 transformers for the project, but the Cinemag mentioned here is interesting as well.

Did you ever resolve your plate voltage mismatch issue? One way is certainly to have better matched tubes.
Another possibility is to add a trimpot to the cathode resistor, and adjust each tube for the same plate voltage ~150V. Something like replacing the 50ohm resistor to 120ohm with a 180ohm trimpot in parallel.


I'm not sure how this works with the CCS, since it should ensure that the current through the tube is constant at 30mA

By the way, that EL84 Head/Speaker amp you had listed is really cool.

My next amp was going to be a SE2A3 following JE Labs' "Radiotron 2A3" Schematic. I'd love to be able to add a headphone output as well, what is the best way of achieving this?

I've seen a few schematics for resistor network "adaptors" you can build which go in-between the speaker outputs and your headphones.

 

[carlman14]

I'd love to be able to add a headphone output as well, what is the best way of achieving this?

The easiest way to add a headphone out to a speaker amp is to have resistors in parallel with the headphone. If your output transformer secondary is 8 ohms, add 8-10 ohm resistors from the left and right connectors on the headphone jack to ground. That way, no matter what ohm headphone you plug in, it will still appear to be roughly 8 ohms connected to the secondary because your headphones will be in parallel to those resistors.