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You know - you are right! I have had it for quite a while and have not listened to it much, so I decided to sell it, put it on ebay, but as I played it while checking it before putting it on sale, I realized it actually had wonderful sound. Apparently that tape is made from a digital source, and that is going to turn some analog lovers away, but I think we should judge the recordings by their sound, not just their technology, so I might actually keep it.

Not really, and if I find time to do that, I will at least explain how to do it. I don't need NAB myself, as I have only one or two tapes in that format and my Crown can play them, but I understand some people's needs.

Yes, it is roughly the same. In this case the 400Hz signal at 320nWb/m results in 500mV output. The heads have about 400 Ohm resistance.

I forgot to mention specifically that the gain was increased by about 10dB.

@@Foxbat9000 Спасибо за ответы! А сколько милливольт выходит с головки и поступает на вход? (чтобы получить 500 милливольт на выходе?)

@@alexanderleymann2981 Approximately 2mV, I did not measure it more accurately.

Unfortunately, there are no reference designators on the board, so it is difficult to discuss the changes. Two components in the EQ circuit are removed and the 47K resistor replaced with a 10K trimpot. The 510 Ohm resistor in the first tube cathode circuit was paralleled with a 360 Ohm resistor for more gain. The .01uF capacitor between the first and the second tubes gets 82,000pF cap in parallel. The input 47K resistor was left there but I will replace it with 100K one, as for the this head it makes more sense, otherwise the pole is at 29KHz, which is a bit too close for comfort. For IEC conversion it might make more sense to leave the 510 Ohm as is, but increase the value of the 680K resistor, perhaps to 1.5 Meg or so, in order to move the main pole to lower frequency. As it is now, the LF response at 31.5 Hz is down about 4-5dB, if you feel you want more bass then do the 680K resistor change instead of reducing the 510 Ohm one.

@@Foxbat9000 Thank you!! Most of this makes sense. Maybe a video part 3 that actually points to specific parts or photo with arrows? I just ordered the board from ebay. Thank you again for your time

@@bobbystefano once I am certain about the final changes, I will definitely do that. But there is no designer out there who would not feel he just must make one more "last" change right as the product is getting released. :) I had been in that loop. :) As I mentioned, I am going to do another round of modifications and hopefully finalize it at that point. Yeah... I know.. :)

I did not measure the output resistance, I was going to take it back to my office for more measurements once the construction was more finalized.

@@Foxbat9000 Let me know when you have some recommended values. I have a spare ReVox B77 MkII which I long ago modified to only run at 15ips. I have been thinking of making it a playback only machine and adding tube repro. I also have a fully balanced B77 Mk II HS, an unbalanced BB77Mk II HS, an MCI JH110B with 1/4 and 1/2 inch stereo headblocks, and a Tascam 52. Keep up the good work.

Thank you! We are a small community and should be helping each other.

Moving along... I already put the prototype in the case and started checking it out. If all goes well it will make its first sounds tomorrow.

That is correct, but on the plus side they are remarkably reliable.

@@Foxbat9000 They are pretty solid. After a full restore, they can run for a long time without any problems.

Do you mean the transmitter or the receiver part? The receiver is widely sold on ebay, but it comes with an ugly transmitter, so I then buy that Sony Beta nice looking controller, that works fine with the receiver.

​@@Foxbat9000The whole setup. I have this machine in my studio. What are the model numbers on the transmitter and receiver and where can I get that cable? Thanks for the info.

@@guyprier6060 Here is the whole unit: www.ebay.com/sch/i.html?_from=R40&_trksid=p2332490.m570.l1313&_nkw=otari+mtr+wireless+remote&_sacat=0 But ask the seller to make sure it will work with your model. I will get the transmitter model number later.

Thank you!​@@Foxbat9000

@@guyprier6060 Not a problem... for the transmitter I am using this: www.ebay.com/itm/386909520279?_nkw=sony+beta+319+remote&epid=1800247407&itmmeta=01J6T3636XJF7MQB75GM2EFDPF&hash=item5a159ac197:g:QwUAAOSwg61mEDk2&itmprp=enc%3AAQAJAAAA0HoV3kP08IDx%2BKZ9MfhVJKnhVlu9UA7Kj1CWwopGcO0Dao9XQCavqNyyggMHqU3R9mxl3KceFKHPuvUBGqZbr%2BKN%2B6E5%2FfsSsFLXLVUrkD6aojnKHBavBtJdlqmopZ8o2TDN7tx97NU6Tn3R%2BMnmI%2B%2F5b2XQ9jRyvMSxAq2gc8WPy8mOe2WmyLWYDgNajehORpGJiKF53Tx%2BUwYM%2FbLSgFy3UU6nV6V3Ufnf1tTx4ZNmUp4UBRUvzOxY9cRYYGwaUR8cwqhLOTj%2BJ2mxPsuzK38%3D%7Ctkp%3ABk9SR8CzmMO2ZA

I can see why that could be the case, I might try it later. Thank you for the tip!

That one is interesting... while still using three triodes in the seemingly similar configuration, it runs the first one outside the feedback loop. That product has good reputation, and yes, it is another candidate.

I will see what I can do... but it looks more and more, as I think about such additions, that perhaps a Part 3 would make sense.

No, it is not even complete yet. Although it worked with its own power transformer on the tester today., so it is alive.

@@Foxbat9000 I was surprised by sound quality even on TH-cam. Waiting for part 2.

@@Gerta789 Maybe it is time to sell the Telefunken and buy an Ampex? :)

@@Foxbat9000 maybe to sell, not to buy

@@Gerta789 You can't sell without someone buying. :)

Well said. Fortunately, my job is an extension of my life-long hobby.

Yes, that is not a problem. I have already done some of that.

@@Foxbat9000 Thank you, that's wonderful! Is this something you would like to do here or would you prefer to PM me?

@@normloo1590 There is no huge secret there, it is a differential passive EQ network. Let me just describe the first level modification here - single EQ, be it NAB or IEC. If you understand sufficiently that level you can start expanding. Let's presume we are doing 15ips. Locate the capacitor C136. If you are doing NAB, leave it alone. If your goal is IEC then you double it. Remove the capacitor C135 (it could actually be consisting of two parts, the second small value one added during the factory trimming process) and replace it with a 5K multi-turn potentiometer. That is it.

@@Foxbat9000 We audiophiles are greedy and wish for " everything" ! Can I acquire the equalization board from you? With settings calibrated for RiAA, NAB, CCIR/IEC, and 30ips.

@@normloo1590 PM me.

I agree it looks kinda strange, especially since there is no clear label or indication, but it works reliably. Interesting to see how the designers approached some tasks.

There is some truth to what you are saying - I am crazy to be in this profession... I should have been a stock broker. :)

That is the 23rd concerto, and I wish I would know, I would have bought it myself. As it is I only have the 24th, which is not my favorite. So I made a copy of a hi-res file.

The original was on the Telefunken.

I would need 5 mile long cables for that, as the AP is in my office. :) But it measures very well, I thought I mentioned it somewhere. From memory the 15ips PB response is about -1dB at 20KHz, and then very flat, just -.5dB at 31.5Hz. The 7.5 ips was about -2dB at 16 KHz, and flat from that point down. The 30 ips response was just about -1 dB at 25 KHz. The RIAA was adjusted on the AP before I took it home, to be well within +/- .1dB across most of the audio band - our standard tolerance. You can see that in the Stereophile review. With responses like that I don't bother writing them down. When I take the record-playback responses on AP I usually make plots. But this is PB-only system here.

Well, it is not possible to make a blanket statement regarding its fitness in other products. It presumes a certain passive EQ circuit configuration, but there is more than one topology used in different phono stages. That configuration itself is not unique (although not universal), but the component values will most likely depend on the particular product design. So each case outside the BAT models would have to be considered separately.

Very observant! :) As I mentioned, there are different versions out there, including one preamp I have that came from literally the first batch of product built - it still goes strong. :) The older models had the capacitor outputs. When I replaced them with high quality custom Lundahl output transformers, we loved the result, so this is the current production configuration. Is it really absolutely best? I am not sure... I love the sound of both, actually. So if someone was shopping for a modification vehicle I would not let that choice dominate. Also, in case of the capacitors you have many options, so you can tailor the sound to your liking. I like the low end of the capacitors better. Regarding the input transformers... they mean more parts in the signal chain, and hence they are necessary evil, I would rather do the direct connection. In this particular case there was no way around them, as the heads have too low output. With that 20dB of additional gain the signal gets into the comfortable range. These transformers are also of very, very high quality, they are among the best you can get, but still, you are better off without them, if you can make that work. It is nice to have that flexibility, though.

Thank you, and yes, I am very proud of it, but it's been dormant for years now. :)

Congratulations on your new purchase, I hope you continue enjoying it! But there is no law that states having more than one is illegal. :) After all, the cost of this project can be as low as $1,500 or so. :)

Yes, there are many ways to skin a cat, but 5 is an odd number - are you sharing a tube between the two channels? We are not going to go into balanced vs. unbalanced debate here, and in one model I do use an unbalanced circuit for the first gain stage. :) I am not a dogmatic.