{"id":5704,"date":"2016-08-25T08:53:39","date_gmt":"2016-08-25T07:53:39","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=5704"},"modified":"2016-08-29T09:37:41","modified_gmt":"2016-08-29T08:37:41","slug":"2756-preamp-from-jose-martins","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2016\/08\/25\/2756-preamp-from-jose-martins\/","title":{"rendered":"27\/56 Preamp from Jose Martins"},"content":{"rendered":"

Jose Martins sent me an email with his recent built on the 27<\/a>\/56<\/a> preamplifier using the gyrator load and these PCBs<\/a>. I recently posted an idea using the lovely 27 IHT valve here<\/a>.<\/p>\n

Here is a picture of the finished preamplifier:<\/p>\n

\"DSC01108\"<\/a><\/p>\n

Hello Ale,<\/p>\n

Here is some photos of my new creation where I used your Gyrators boards.<\/p>\n

This is a line 27\/56 preamplifier. Working great with your Gyrator boards. I\u2019m planning to use also in near future a second output with Magnequest parafeed transformers B7\/15K.<\/p>\n

I built \u00a0this project in old Antique Sound Lab AQ2001 inox steel chassis that I have for some years in my garage.<\/p>\n

The filament supply for tubes are regulated and noise of this preamplifier is very low even with old Arcturus 127 triodes from \u00a01923. It is very important to connect the cathode of these old tubes to the filament.<\/p>\n

I can also use 56 triodes to get more gain with no modification. Now I must test all my stock of 27 and 56 triodes. I\u2019m very happy with the sound even compared with others DHT tube preamplifiers I have (26, 4P1L, VT-25, 1G4, RE084, Ba, Ca, TM2).<\/p>\n

I\u2019m very happy with your boards. Thank you for your great products.<\/p>\n

Best Regards<\/p>\n

Jos\u00e9 Martins<\/p>\n

Ps: please excuse my bad English.<\/p><\/blockquote>\n

 <\/p>\n

This preamp looks great, well don Jose. BTW: your English is really good, so nothing to apologise of. I hope to get some circuit diagrams and description from Jose to update the post. In the mean time, here are some detailed pictures of this fantastic build:<\/p>\n

\"Inside <\/a>
Inside the preamp <\/div> <\/div>
\"Gyrator <\/a>
Gyrator Board <\/div> <\/div>
\"Gyrator <\/a>
Gyrator board <\/div> <\/div> <\/div>
\"DSC01111\" <\/a> <\/div> <\/div> <\/div> <\/div>\n

Update 1<\/h1>\n

Here are some further notes from Jose:<\/p>\n

“The preamplifier is based in your 27 circuit, but I not used fixed bias with battery on the grid of the tubes, instead I used a auto bias with an 1.5K\u03a9 resistor with the cathode bypassed cap. After tried several types \u00a0of caps I chose the Sanyo OSCON\u00a0 100uF \/16V.<\/p>\n

The volume pot is a Alps Black 40mm 50K\u03a9 log directly to the grid of the tube.<\/p>\n

For HT supply I used the original tube power supply from original ASL AQ2001, tube rectifier 5Y3 and tube regulated with 12AX7 and 6V6, with a few changes in the circuit and in type of filter caps. I think with the gyrators the power supply could be more simple but in this project i used what I have on hand.<\/p>\n

In these old triodes it is crucial to connect the cathode directly to filament according to the instructions of data sheet. Without this connection the hum noise is very loud.<\/p>\n

I decide to supply the filament with DC because I already have all the components to make the regulators and to reduce as much as I can the noise. First tried the current regulators but I got too much hot from regulators and power resistors and never have the right tension between different tubes, so finally I decide to built a voltage regulator. I don\u2019t like voltage regulators but these are indirect tubes and the quality the filament supply don\u2019t influence much the sound of these kind of tubes like in DHT tubes.<\/p>\n

Now the hot generated by the chips (LT1084) are acceptable when used with 27 triodes (1,75A) for a long period. Besides that, I can easily change between the 27 and 56 with no need of any adjustment in the regulators. The ripple with these voltage regulators is\u00a0negligible and contribute to a low noise preamplifier.<\/p>\n

The sound is better than I expected from these old IHT tubes.<\/p>\n

Another important aspect to be taken into account when using these old tubes is the bad contacts of the pins that make the tubes generate all kind of strange noises. After a good cleaning and re-solder all the pins these strange noises are gone.<\/p>\n

Some very old tubes are microphonic and capture many external interferences, but these interferences can be attenuated or completely eliminated with a electrostatic shield. The michophonic in manageable with some care during the construction. In my case only four tubes from my stock of \u00a0the oldest 27 triodes have high level of microphonic.<\/p>\n

I adjusted the gyrators boards 5mA with 27 triodes and with 56 the plate current low a little bit to 4,5mA that is in line with the specs on the data sheet.<\/p>\n

I tried this preamplifier with some power amplifiers (valve and transistor) and in all cases the sound is very detailed and musical with the pleasant and magical sound of these old triodes.<\/p>\n

I recommend very much your boards and this circuit that give me great results. I have new ideas to use your boards again with other old tubes I have.<\/p>\n

Best Regards<\/p>\n

Jos\u00e9 Martins<\/p>\n

Portugal”<\/p><\/blockquote>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Jose Martins sent me an email with his recent built on the 27\/56 preamplifier using the gyrator load and these PCBs. I recently posted an idea using the lovely 27 IHT valve here. Here is a picture of the finished preamplifier:<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[911,156],"tags":[897,933,934,697,932,131,44,935,576,936],"class_list":["post-5704","post","type-post","status-publish","format-standard","hentry","category-gyrator-pcb","category-pre-amplifier-valves","tag-27-preamp","tag-27-tube","tag-27-valve","tag-2sk170","tag-56-preamp","tag-dn2540-gyrator","tag-gyrator","tag-gyrator-preamplifier","tag-hi-fi-interconnect","tag-hi-fi-preamplifier"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-1u0","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/5704","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/comments?post=5704"}],"version-history":[{"count":4,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/5704\/revisions"}],"predecessor-version":[{"id":5731,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/5704\/revisions\/5731"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=5704"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=5704"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=5704"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}