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Retrofits and Conversions
Amp Supply LA-1000
- LA-1000 Retrofit - K4POZ 10/2006
Dentron Clipperton L and Clipperton QRO
Notes: The Clipperton L and the Clipperton QRO are both a beautiful table top near legal limit amplifier and will perform to full specifications when properly retrofitted with the GI-7B tubes. They are easier to retrofit than the MLA-2500 and will give nearly identical performance. Please read all the notes below on the MLA-2500 before you decide to start this project.
- Clipperton L Retrofit - W4EMF 2003
- Clipperton QRO Retrofit - W4EMF 2001
Dentron GLA-1000
Notes: The GLA-1000 is a beautiful little amplifier and will perform to full specifications when properly retrofitted with the GI-7B tube. It is important to note that, as with any retrofit, you should NOT expect more out of this amplifier than it was designed to provide. You can not get more power output from this amp than the power supply is capable of providing. Also, the retrofit of the GLA-1000 (this applies to most of the other sweep tube amp retrofits too) requires changing the power supply to a voltage doubler. When you do this, the plate voltage will be higher. Obviously if you can not get more power from the power supply, then the plate current will be lower. What this means is that the plate load impedance is going to change. What that means is that the Pi-network will no longer provide a proper match to the antenna jack. You can get the amp to work but it will not come up to full output. I have provided some general guidelines for establishing the proper tap points on a tank coil here http://gs35b.com/discussion.html. There are other opinions on this subject so please understand this is just one of them. I am not in a position to hold your hand through a project like this so be well aware of what you are getting yourself into before taking this on. W4ZT
- GLA-1000 Retrofit - W4EMF 2002
- GLA-1000 Retrofit - PA0FRI
- GLA-1000 Retrofit Page - N8GPQ
Dentron MLA-2500
Notes: The MLA-2500 is a beautiful table top near legal limit amplifier and will perform to full specifications when properly retrofitted with the GI-7B tubes... BUT... this is NOT a project for the faint of heart. If you do not have experience doing metal work, schematic reading, figuring things out from pictures, troubleshooting and intuitive layout design based on available components, you may not want to take this project on. You are not going to find a list of detailed instructions here for doing this retrofit. You are not going to find a detailed list of parts for doing this retrofit. You will find a detailed schematic that reflects most of the changes that can be made but not necessarily all of them. If you do not find the information you are looking for here, I am afraid that I do not have it. Carefully study the pictures in these retrofits. You should also study other MLA-2500 retrofits done using other tubes. All of this study will give you better ideas for doing your own work. W4ZT
- MLA-2500 Retrofit - W4EMF 2001
- MLA-2500 Retrofit - W8SLC 7/2007
- MLA-2500 Schematic and modifications - W4ZT 7/2007
- MLA-2500 Retrofit - W4EMF 1/2008
- MLA-2500 Retrofit - N4BWD 1/2008
- MLA-2500 Retrofits using other tubes - W4EMF (a look at many of Lawson's projects)
- MLA-2500 Unusual problems encountered - W4EMF (worth a look no matter what amp you work on)
Drake L4B
- L4B Retrofit - W4EMF 2002
Heathkit SB-200
- SB-200 Retrofit - K4POZ 7/2006
- SB-200 Retrofit - K4UDR 9/2006
- SB-200 Six Meter Conversion and Retrofit - N4LR and W4ZT 6/2007 in progress
Heathkit SB-230
| Please note: Although we show you how the GI-7B can be used to retrofit the SB-230 in the original conduction cooled configuration, we feel it is only fair to tell you that the tube will not cool as well as a conduction cooled amp as it will with the factory cooler on the tube and a small fan blowing on it. If you still want to do the conduction cooled retrofit, we can supply the new cooler as well as the socket. Even if you do the retrofit as a conduction cooled amp, it is wise to blow a small amount of air around the tube to keep the base of the tube properly cooled. It is also worth mentioning that even though the SB-230 has been retrofit with the GI-7B standing vertical, that is not the best or recommended way of doing it. Our experience indicates that there is much less work and much better operation if the tube is mounted horizontally against the right side wall. We do have sockets and can provide the cooler for the conduction retrofit but We do NOT provide complete KITS for this retrofit. |
- SB-230 Retrofit - one tube, Conventional Cooling - K4POZ 2008 - Detailed pictures of the work
- SB-230 Retrofit - one tube, Conduction Cooled - K4POZ and W4ZT 2007
- SB-230 Retrofit Schematic and mods - K4POZ and W4ZT (462 Kb PDF updated 8/10/08)
- SB-230 Retrofit - one tube mounted vertical - W5KG 10/2006
- SB-230 Retrofit - two tubes mounted vertical - K4POZ 9/2006 - This is NOT the way to go!
Yaesu FL-2000
- FL-2000B Retrofit and conversion to Six Meters - W4LK 2007
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| Construction details
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GI-7B Tubes and Parts Suppliers
GI-7B Tubes - I have many people ask about these tubes and where to buy them. You can purchase them from any number of dealers, most of which are outside the USA. The prices listed by these dealers usually does NOT include the shipping charge so be sure to check that before ordering. Also, be sure that the price includes the anode cooler. You don't want to pay full price for a tube that doesn't have the anode cooler. The GI-70 does NOT have a cooler.
GI-7B Sockets - See the pictures at the bottom of this page.
Bias Boards - variable bias for your amp. Click here to go to the Bias Board page.
GI-7B tubes and other parts - I have purchased from each of these suppliers. I will NOT list a supplier that I have had bad experience with or that I have not had dealings with.
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