APPJ EL84 SE mini Tube Amp, PA0901A - Page 7 - diyAudio
Go Back   Home > Forums > Commercial Sector > Manufacturers > Twin Audio
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Twin Audio Twin Audio is a manufacturer of hand made audiophile tube amplifiers.

Reply
 
Thread Tools Search this Thread
Old 5th October 2016, 04:23 PM   #61
diyAudio Member
 
Join Date: Aug 2010
Location: France, Normandy
Many thanks PCan.

May I suggest you to summarize your suggestions on a short list to ease the implementation and verification of mods ?

Gro
  Reply With Quote
Old 5th October 2016, 08:05 PM   #62
pcan is offline pcan  Italy
diyAudio Member
 
Join Date: Dec 2015
I've done the following modifications to my PA0901A with PCB dated 2011.11.11:
1) Replaced the 2A timed 5x20 fuse with a 1A timed 5x20 fuse. According to the switching controller datasheet, a fast-acting 3.15A fuse may be used.
2) Installation of mains-rated (CE-marked) wires from the power outlet to the PCB L and N contact points. I soldered the wires directly on the PCB traces (back side), because the section is bigger than the original holes. On the free L and N holes, I installed a S20 275V varistor for sourge protection. I also added a layer of kapton insulation tape on the live area of the PCB.
3) Removal of the wire connected between the mains outlet ground terminal and the PCB. Installed a 1 sqmm green-yellow wire from the mains outlet ground terminal to the top screw at the corner nearest to the RCA inputs. The wire is terminated with a flat electrical lug; the lug is securely trapped between the top plate and the bottom case and does have good electrical contact with both metal parts.
4) Replaced the two series-connected 1206 560K SMD resistors between live and neutral with 3 series connected 1/4w 330K trough-hole metal film resistors.
5) added kapton insulation on the bottom cover above the aluminium heatsink. This heatsink is connected to the primary side of the SMPS and it has a 2mm clearance to the metal bottom cover. The cover has a ventilation hole exactly over one of the fins. That's simply insane, I was speechless when I discovered this safety blunder.
6) Removed the big primary side capacitor (270uF 400V Nichicon GN, with a PCB adaptor) and replaced with a 100uF 400V Nichicon VZ, soldered on the main PCB. The Nichicon GN is a good and expensive capacitor, but I replaced it with a genuine Nichicon bought from RS Components to increase the clearance from the heatsink and because I was not 100% sure about the source of the original capacitor. This is the only critical electrolytic capacitor in this amplifier.
7) Replaced the two RIFA 300V rated coupling capacitors with standard 630V film capacitors. 300V is the bare minimum. 630V (or even 400V) gives a bit of headroom. Fancy Hi-Fi capacitors are not needed with the tiny output transformer (and the global feedback path is trough a SMD ceramic capacitor).
8) Modified the PCB to install a 1W 1K resistor on both EL84 g2 (pin 9) as protection measure. This is not strictly required, but the PCB modification is easy and clean.
9) Removed the 10K SMD resistors across each RCA input and ground. They lower the input impedence unnecessarily (the declared impedence is 50K, but without the resistors).
  Reply With Quote
Old 6th October 2016, 10:11 AM   #63
diyAudio Member
 
Join Date: Aug 2010
Location: France, Normandy
Thanks PCan.
Things are now clearer for me, that will make it easier to apply on my amp.
I guess it's the same for other owners.

Cheers,

Gro
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
APPJ PA0901A() schematics fx19979 Tubes / Valves 1 24th August 2013 05:27 AM
APPJ PA0901A / Miniwatt N3 schematics fx19979 Tubes / Valves 0 23rd February 2013 09:14 AM
Replacing a driver tube in an existing EL84 SE Amp corbato Tubes / Valves 29 16th February 2003 06:33 PM


New To Site? Need Help?

All times are GMT. The time now is 10:36 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki